[DAY 59] 60 DAY RAPID REVISION (RaRe) SERIES for UPSC Prelims 2025 – SCIENCE & TECHNOLOGY, CURRENT AFFAIRS & CSAT TEST SERIES!

Solution (b)

Explanation:  

• Experiments aboard satellites are typically referred to as space-based experiments or on-orbit experiments, rather than analog missions.
• Analog missions are field tests conducted on Earth in locations that mimic the extreme conditions of space environments, such as high altitudes, extreme cold, or barren landscapes. 
• These missions help researchers and astronauts test equipment, study human performance, and develop protocols for future space exploration. India’s first Mars and Moon Analog Mission was conducted in Ladakh, a region resembling Martian and lunar terrain. (Option (b) is correct)
• Testing the deployment of orbital spacecraft typically involves simulations in specialized facilities or space-based tests. 

Solution (a)

Explanation:  

• Mission Divyastra marks the advancement of India’s Agni-5 program by integrating MIRV technology, which allows a single missile to carry multiple warheads that can hit different targets independently. This represents a significant enhancement of India’s strategic deterrence capabilities. (Option (a) is correct)
• The Agni-5 missile is an intercontinental ballistic missile (ICBM) and is not a hypersonic missile. While hypersonic missiles travel at speeds exceeding Mach 5 and have maneuverability, the Agni-5, though very fast, does not fall into this category.

Solution (c)

Explanation:  

• The RBI focuses on monetary policy, financial regulation, and digital payment systems. The RBI does explore the role of AI in the banking sector, particularly in fraud detection and improving payment systems.
• ISRO is India’s premier space research agency and focuses on satellite technology, space exploration, and applications of AI in space missions.
• NITI Aayog, the Indian government’s policy think tank, has issued the National Strategy for AI and the Responsible AI for All report. These documents emphasize the use of AI for social and economic inclusion, innovation, and ensuring trustworthiness in AI applications. The reports provide guidelines for leveraging AI in sectors like healthcare, education, agriculture, and urban development while addressing ethical concerns. (Option (c) is correct)
• MeitY works on policies related to digital governance, cybersecurity, and AI infrastructure. MeitY supports AI development under initiatives like the AI Pe Charcha series and digital innovation frameworks.

Solution (b)

Explanation:  

• The Venus Orbiter Mission (VOM) is designed to study the atmosphere, surface topography, and interaction with the Sun, including phenomena like Venusian airglow, solar X-ray spectrum, and sub-surface characteristics. These objectives align with addressing gaps left by earlier missions and advancing our understanding of Venus’s complex environment.
• A key feature of the mission is its ability to provide uniform coverage of Venus, overcoming the limitations of earlier missions that had narrow spatial coverage, such as focusing only on the south polar region or equatorial belt. This comprehensive dataset will help map global phenomena like winds, waves, and chemical abundances.  (Option (b) is correct)
• The mission includes one international payload and two collaborative payloads involving Indian and international entities, as recommended by the Experts Review Committee. This international collaboration ensures that the mission benefits from diverse scientific expertise and advanced instrumentation. 

Solution (c)

Explanation:

• The Council of Europe Framework Convention on Artificial Intelligence and Human Rights, Democracy, and the Rule of Law is a landmark treaty aimed at ensuring that AI systems are developed and utilized in ways that uphold human rights, democratic principles, and the rule of law.
• This convention, opened for signature on September 5, 2024, is recognized as the first international legally binding treaty in the field of AI.
• The United States signed the convention during the opening ceremony in Vilnius, Lithuania, on September 5, 2024.

The primary objective of the convention is to ensure that AI systems are consistent with human rights, democracy, and the rule of law, while also promoting technological progress and innovation. (Option (c) is correct)

Solution (d)

Explanation:  

• The Biopharmaceutical Alliance was launched by India, Japan, South Korea, the United States, and the European Union (EU) to address drug supply shortages and enhance supply chain resilience in response to the challenges exposed during the COVID-19 pandemic. 
• The inaugural meeting took place in San Diego, California, during the Bio International Convention 2024, highlighting a collaborative effort among these nations to strengthen global health security. (Option (d) is correct)

Solution (a)

Explanation:  

• The Wassenaar Arrangement focuses on promoting transparency and responsible controls over the transfer of conventional arms and dual-use goods and technologies. India became the 42nd member of this grouping in 2017, marking a significant step in its integration into global non-proliferation regimes. Membership helps India access advanced technology and strengthens its export controls. (Option () is correct)
• The Australia Group focuses on controlling the export of chemical and biological weapons-related technologies to prevent their misuse. India joined this group in 2018.
• The MTCR aims to prevent the proliferation of missile and unmanned aerial vehicle (UAV) technologies capable of carrying weapons of mass destruction (WMD). India joined this regime in 2016 as its 35th member.
• The NSG controls the export of nuclear-related technology to prevent nuclear proliferation. Despite India’s efforts, it is not yet a member of the NSG due to opposition from some member countries.

Solution (c)

Explanation:

• There are three criteria of the International Astronomical Union (IAU) for a full-sized planet are:
  • It is in orbit around the Sun.
  • It has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
  • It has “cleared the neighbourhood” around its orbit.

Pluto meets only two of these criteria. It has not managed to clear its neighbourhood. Clearing the neighbourhood means that the planet has become gravitationally dominant so that there are no other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence, in its vicinity in space. But Pluto shares its orbital neighbourhood with Kuiper belt objects such as the plutinos. So, option c is correct.

Solution (d)

Explanation:  

• SSLV is a newer and smaller launch vehicle designed for launching small satellites into low Earth orbits (LEO) at short notice. While versatile in its category, it is not considered ISRO’s workhorse and is focused on catering to the growing small satellite market.
• GSLV is designed primarily for launching geostationary satellites and heavier payloads into geosynchronous transfer orbits (GTO). It is mainly used for communication and meteorological satellites.
• Formerly known as GSLV Mk-III, LVM-3 is ISRO’s heaviest and most powerful launcher, capable of launching large satellites into GTO and low Earth orbits. It is also the designated launch vehicle for human spaceflight missions under Gaganyaan. 
• PSLV is ISRO’s workhorse, known for its versatility in launching a wide range of payloads, including Earth observation, navigation, and small satellites into various orbits, including polar and geostationary orbits. It has achieved numerous successful launches and has been instrumental in missions like Chandrayaan-1 and Mars Orbiter Mission (Mangalyaan). (Option (d) is correct)

Solution (b)

Explanation:

• Nanotechnology is the study and manipulation of matter at dimensions ranging from 1 to 100 nm (not 1,000 nm) where unique phenomena allow for novel applications. Nanomaterials enable lighter, stronger, and more functional materials while nanoelectronics power faster, smaller computing. Nanotech is being integrated into various industries such as food packaging, cosmetics, textiles, chemicals, automotive, aerospace, and agriculture. Hence, statement 1 is not correct.

Graphene has been hailed by many as the “wonder material” of the 21st century as this carbon-based material is nearly 200 times stronger than steel, flexible, nearly transparent, and highly conductive to heat and electricity. Since graphene is just a single layer of carbon atoms connected in a hexagonal pattern, it is also extremely thin and lightweight, and therefore an attractive material for nanotechnology applications. Hence, statement 2 is correct.

Solution (a) 

Explanation: 

Gravitational Waves are ripples or disturbances in the fabric of spacetime caused by the acceleration or movement of massive objects. They have a much lower frequency range compared to electromagnetic waves. Hence Statements 1 is correct. 

 Gravitational waves are different from other types of waves, such as electromagnetic waves, because gravitational waves do not require a medium to propagate. They can travel through empty space without being significantly affected or diminished. Hence Statement 2 is incorrect 

Solution (d) 

Explanation 

Space distance is measured in terms of light years. Since the speed of light is known to be constant throughout the universe and for high precision, astronomical distances are expressed in terms of light-years. The fastest light can move is in a vacuum. The symbol for the speed of light in a vacuum, c, is 3×108 m/s. z Astronomers calculate the distances of stars and other celestial objects in the time it takes for light to reach us since estimating distances in miles or kilometres is inadequate on the scale of the cosmos. Hence option (d) is the correct answer. 

Solution (d) 

Explanation: 

The evolved Laser Interferometer Space Antenna (eLISA) mission aims to conduct the first ever space-based study of the gravitational universe. It includes researchers from eight different European nations, including Denmark, France, Germany, Italy, The Netherlands, Spain, Switzerland, and the United Kingdom, as well as some US-based ones. z The European Space Agency accepted the “The Gravitational Universe” subject (with eLISA as the anticipated implementation) and chose it as a science theme for the third large-class mission to be launched in 2034 as part of the agency’s Cosmic Vision research programme. Hence option (d) is the correct answer. 

Solution (b) 

Explanation: 

The LIGO detectors detected the first gravitational waves produced by two giant merging blackholes in 2016. In 2017, the Nobel Prize for physics was awarded to the LIGO-VIRGO collaboration for their detection of gravitational waves arising from the merging of two black holes. Hence Option (b) is the correct answer. 

Solution: (d) 

Explanation:

An item warps the space around it more dramatically the more large it is. Like a big ball lying on a rubber sheet, the sun, for instance, is large enough to bend space throughout our solar system. Because of this, Earth and the other planets orbit it in bent paths. Hence Statement 1 is correct. 

General Theory of Relativity showed that space and time are malleable or flexible, and ever expanding predicted that our universe was ever expanding. The theory of relativity states that massive objects distort spacetime around it. And since photons travel the shortest distance between two points, light appears to be bent when it travels through the distorted spacetime of a massive object. Hence Statement 2 is correct. 

An item warps the space around it more dramatically the more large it is. Like a big ball lying on a rubber sheet, the sun, for instance, is large enough to bend space throughout our solar system. Because of this, Earth and the other planets orbit it in bent paths. Hence Statement 3 is correct.

Solution (c)

Explanation:

• Syngas is a mixture of hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2). Syngas can be produced from underground coal reserves through the process of coal gasification. Syngas can also be produced from sewage, saw-dust, scrap wood, newspapers and other biomass wastes. Hence Statement 1 is correct.
• Syngas can be used as a feedstock for the production of methanol, fertilizers, ammonia, urea etc. The syngas, obtained from coal gasification can be used in a variety of applications such as in the production of electricity and making chemical products such as fertilizers. Hence Statement 2 is correct.

Solution (c)

Explanation:

• The BEC is formed by cooling a gas of extremely low density, about one-hundred-thousandth the density of normal air, to super low temperatures.  Hence statement 1 is incorrect.
• Bose-Einstein Condensate (BEC) is the fifth state of matter whose existence was predicted by Albert Einstein and Indian mathematician Satyendra Nath Bose in the early 1920s. It is formed when atoms of certain elements are cooled to near absolute zero (0 Kelvin/-273.15 Celsius). At this point, all atoms become a single entity with quantum properties wherein each particle also functions as a wave of matter. Hence statement 2 is incorrect. 
• BECs are extremely fragile. The slightest interaction with the external world is enough to warm them past their condensation threshold. This makes them nearly impossible for scientists to study on Earth. Hence statement 3 is correct. 

Solution (a)

Explanation:

• • Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power is the second-largest source of low-carbon electricity today.
  •  A major environmental concern related to nuclear power is the creation of radioactive wastes such as uranium mill tailings, spent (used) reactor fuel, and other radioactive wastes. These materials can remain radioactive and dangerous to human health for thousands of years.  Hence Statement 1 is correct.
  • The nuclear accidents does not commonly occur, but when it happens, it can lead to significant consequences to people and the environment. The prime example of a “major nuclear accident” is one in which a reactor core is damaged and significant amounts of radioactive isotopes are released in air, such as in the Chernobyl disaster in 1986 and Fukushima nuclear disaster in 2011.  Hence Statement 2 is correct.

• Used nuclear fuel has long been reprocessed to extract fissile materials for recycling and to reduce the volume of high-level wastes. A significant amount of plutonium recovered from used fuel is currently recycled into MOX fuel. Hence Statement 3 is incorrect.

Storage and disposal of used fuel is a major hindrance in nuclear energy. Used nuclear fuel is kept in either wet or dry storage facilities, before being recycled or disposed of. When used fuel is taken out of a reactor, it is both hot and radioactive and requires storage in water to allow the fuel to cool. Hence Statement 4 is correct.

Solution (b)

Explanation:

• Defence Research and Development Organisation (DRDO) has recently carried out successful maiden flight test of Long Range Glide Bomb (LRGB) GAURAV from Su-30 MK-I platform of the Indian Air Force (IAF). 
• GAURAV is an air launched 1,000 kg class glide bomb capable of hitting targets at long distance. After being launched, the glide bomb steer towards the target using highly accurate hybrid navigation scheme with a combination of INS and GPS data. 

It is an Air to Surface LRGB with conventional warheads to destroy enemy air strips, bunkers, hard installations, buildings etc. It is designed to integrate with fighter aircrafts. It consists of an Inertial Navigation based guidance system with Digital Control. Hence option b is correct.

Solution (b)

Explanation:

• Ballistic and cruise missiles are advanced weapons designed to deliver warheads over long distances. Ballistic missiles are launched into the upper atmosphere and then re-enter the Earth’s atmosphere to strike the target. Cruise missiles, on the other hand, are designed for sustained flight within the Earth’s atmosphere. Cruise Missile fly within the earth’s atmosphere and use jet engine technology. Hence Statement a is correct.
• Both cruise missiles and ballistic missiles can be launched from aircraft, ships, and submarines in addition to land-based silos and mobile platforms. Hence Statement b is incorrect.
• Payload capacity is limited in Cruise missiles. Cruise missile usually carries a single payload while Ballistic missiles can carry more than one payload (Multiple Independently targetable Re-entry Vehicle). Hence Statement c is correct.

BrahMos is a universal long range supersonic cruise missile system. The Agni-V is an Indian intercontinental ballistic missile (ICBM) with a range of over 5,000 km. Hence Statement d is correct.

Solution (d)

Context:

• The Union Home Minister recently unveiled the HEALD Initiative to combat liver diseases across India. In this context, UPSC can a question about the initiative.

Explanation:

• HEALD (Healthy Liver Education and Alcohol-associated Liver Disease Prevention) is a first-of-its-kind nationwide initiative aimed at tackling liver disease in India. It was launched by the Institute of Liver and Biliary Sciences (ILBS). It is envisioned as a multi-sectoral program combining public education, early screening, psychological and medical treatment of alcohol use disorder, and liver disease management. Hence, statements 1 and 2 are correct.

• The initiative helps to tackle the disease through awareness, prevention, rehabilitation, and policy integration. It also aims to reduce the stigma surrounding alcohol dependence by integrating mental health support, community outreach, and policy reform into liver care. The initiative is grounded in the principle that “behind every failed liver lies a missed opportunity” and HEALD seeks to ensure no such opportunity is lost again. Hence, statements 3 and 4 are correct.

Solution (d)

Context:

• Recent research by University of Texas (UT) Health San Antonio has found that transposon activation may be a key factor in the progression of Alzheimer’s disease. In this context, a question can be asked by asked by UPSC about jumping genes which is associated with it.

Explanation:

• Jumping genes, scientifically known as transposons, are mobile genetic elements that can move from one location to another within the genome. They were first discovered by Barbara McClintock, who won the Nobel Prize in 1983 for this work. The most common type of jumping genes is retrotransposons, especially LINE-1 elements, which replicate through an RNA intermediate and use reverse transcriptase to reintegrate into DNA. Hence, statements 1 and 2 are correct.

In humans, transposons make up nearly 50% of the genome, and while most are inactive, some retain the ability to “jump” and cause genomic instability. Normally, the activity of these elements is tightly controlled by the body through epigenetic mechanisms, but in aging or diseased brains, especially in neurodegenerative conditions like Alzheimer’s, these controls can weaken. Hence, statement 3 is correct.

Solution (b)

Context:

• Despite multiple efforts to contain the spread of communicable diseases, Kerala continues to report a surge in Hepatitis A cases. In this context, a question about the disease can be asked by UPSC.

Explanation:

• • Hepatitis A is a very contagious liver disease. It is a viral infection that happens after exposure to the hepatitis A virus (HAV). The infection causes inflammation in the liver. One can get hepatitis A from:
    • drinking unclean water
    • eating food that’s been washed or grown in unclean water
    • eating food that’s been handled by an infected person

• close physical contact with an infected person, including having sex and sharing needles to take drugs. Hence, statement 1 is correct and statement 2 is not correct.

No specific treatment exists for hepatitis A. Our body will clear the hepatitis A virus on its own. In most cases of hepatitis A, the liver heals within six months with no lasting damage. A safe and effective vaccine is available to prevent hepatitis A. Hence, statement 3 is correct.

Test explained

Solution (c)

Context:

• Researchers at Kyoto University conducted a Phase I/II clinical trial to assess the safety and side effects of stem cell therapy using dopaminergic progenitors derived from human induced pluripotent stem cells (iPSCs). In this context, a question can be asked by UPSC about the iPSCs.

Explanation:

Stem cells are undifferentiated primitive cells capable of developing into specialised cells like blood, muscle, or liver cells. iPSCs are pluripotent stem cells generated from adult somatic cells (like skin or blood). They are reprogrammed to an embryonic-like state, allowing them to develop into any human cell type. They are valuable in drug testing, disease modelling, and transplantation medicine. Hence, statements 1 and 2 are correct.

Solution (c)

Context:

• Earth Day takes place every year on 22 April and is one of the biggest environmental protest movements on the planet. Thus, a question can be asked by UPSC about the day.

Explanation:

• Earth Day is observed annually on April 22. The official theme for Earth Day 2025 is “OUR POWER, OUR PLANET”. This year’s message focuses on the need to shift rapidly to renewable energy, urging individuals, businesses, and governments to triple clean energy production by 2030. The first Earth Day was celebrated on April 22, 1970, initiated by U.S. Senator Gaylord Nelson as a national teach-in on environmental issues. Hence, statements 1 and 2 are correct.

Solution (c)

Context:

• India, the world’s second-largest emitter of N₂O after China, faces climate risks as N₂O has 300 times the global warming potential of CO₂. In this context, basic details related to Nitrogen can be asked by UPSC.

Explanation:

• Nitrogen is the most abundant atmospheric gas, constituting ~78% of Earth’s atmosphere. Nitrogen is vital for forming DNA, ATP (cellular energy currency), proteins, chlorophyll, and acts as a neurotransmitter via nitric oxide (NO). Hence, statement 1 is correct.

• Atmospheric nitrogen (N₂) is inert and unusable by plants or animals. Plants rely on diazotrophs (N-fixing bacteria) through symbiotic association (e.g., in legumes). Nitrifying bacteria convert ammonia into nitrites (NO₂⁻) and then nitrates (NO₃⁻) – the form plants can absorb. Denitrification returns excess nitrates back to the atmosphere, maintaining the natural nitrogen cycle. Hence, statement 2 is correct.

• Haber-Bosch Process, developed in the early 20th century, allowed industrial fixation of nitrogen to produce ammonia. It uses fossil fuels, high heat and pressure, and an iron catalyst. It enabled synthetic fertiliser revolution, which contributed to Green Revolution and exponential population growth. Hence, statement 3 is correct.

Solution (a)

Context:

• The Supreme Court recently directed the National Environmental Engineering Research Institute (NEERI) to conduct an assessment of the nearby glass industries that are impacting Taj Mahal at Agra in Uttar Pradesh. In this context, UPSC can ask a question about NEERI.

Explanation:

• The CSIR-National Environmental Engineering Research Institute (CSIR-NEERI) is a research institute created and funded by the Government of India. It was established in 1958 with a focus on water supply, sewage disposal, communicable diseases, and to some extent, on industrial pollution and occupational diseases found commonly in post-independent India. Hence, statement 1 is correct.

• NEERI is a pioneer laboratory in the field of environmental science and engineering and is a constituent laboratory of the Council of Scientific and Industrial Research (CSIR). It falls under the Ministry of Science and Technology of the central government and its headquarter is located in Nagpur. Hence, statements 2 and 3 are not correct.

Solution (d)

Context:

• The Poas volcano, one of Costa Rica’s most popular tourist attractions, erupted recently. In this context, a question about the location of the volcano can be asked by UPSC.

Explanation:

Poas is one of Costa Rica’s most active volcanoes, which is located in Central America. The volcano is located within the Poas Volcano National Park. It is a composite stratovolcano with an irregular complex form and a basal area of about 400 sq.km. It rises to 2,708 metres above sea level. It has been formed from adjoining eruptive centres with large collapse craters. Its main crater is about 1.5 km wide and 300 meters deep, one of the largest active craters in the world. Hence, option d is the correct answer.

Solution (a)

Context:

• The Jwaneng Diamond Mine is the richest diamond mine globally, with an estimated value of 1 billion euros. In this context, a question can be asked by UPSC about the location of mine.

Explanation:

Jwaneng Diamond Mine, dubbed the ‘Prince of Mines,’ is located in Botswana (Africa). It is the world’s richest diamond mine by value. The mine lies on the edge of the Kalahari Desert. It is situated in an ancient volcanic crater about 170 km southwest of Botswana’s capital, Gaborone. The mine is operated by Debswana, a joint venture between De Beers, a leading diamond company, and the Botswana government. Hence, option a is the correct answer.

Solution (b)

Context:

• The Ministry of Micro, Small and Medium Enterprises (MSMEs) recently stated that the turnover of Khadi and Village Industries (KVI) surpassed Rs 1.7 lakh crore in the financial year 2025 (FY24- 25). In this context, UPSC can ask a question about KVIC.

Explanation:

• Khadi and Village Industries Commission (KVIC) is a statutory body established under the Khadi and Village Industries Commission Act of 1956. It is charged with the planning, promotion, organisation and implementation of programmes for the development of Khadi and other village industries in rural areas in coordination with other agencies engaged in rural development wherever necessary. At the state level, Khadi & Village Industries Boards were set up to effectively implement the schemes of KVIC in their respective states. Hence, statements 1 and 3 are correct.

• • It is an apex organization under the Ministry of Micro, Small, and Medium Enterprises, with regard to khadi and village industries within India. The functions of the KVIC are as follows:
    • To build a strategic reserve of raw materials and implements for supply to producers.
    • To create common service facilities for processing raw materials as semi-finished goods and provisions for facilities for marketing KVI products.
    • To enhance the sale and marketing of Khadi and other products of village industries or handicrafts.
    • To be responsible for encouraging and promoting research in the production techniques and equipment employed in the Khadi and Village Industries sectors.
    • To provide financial assistance to institutions and individuals for developing and guiding the Khadi and Village industries through the supply of designs, prototypes, and other technical information.

• To assure the genuineness of the products and to set standards for the quality of products from Khadi and Village Industries. Hence, statement 2 is not correct.

Solution (d)

Explanation: 

Assumption 1 is incorrect. The passage states, “…a country’s soft power rests on its resources of culture, values, and policies.” There could be a relation between a country’s soft power and the size of its economy. However, in the context of this passage, we cannot say that economy is the ultimate source ofsoft power of a country. Hence, this assumption is not correct.

Assumption 2 is incorrect. The passage states, “…a smart-power strategy combines hard and soft-power resources.” The author does not accord primacy to one over the other. He advocates a smart mix of both hard power and soft power. Hence, this assumption is not correct.

Assumption 3 is incorrect. The passage states, “…as authoritarian states today use new cyber technologies and other means to disrupt political processes in democracies, questions arise about the boundaries of soft power…” This means that the role and scope of soft power is under examination, but not that its importance has necessarily reduced; it just needs to be reviewed accordingly. Hence, this assumption is not correct.

Solution (c)

Explanation: 

Option (a) is incorrect. The passage only mentions technology in the context of its use by authoritarian states to disrupt political processes in democracies. This is not the soft power which is the core theme of the passage. Hence, this option is not correct.

Option (b) is incorrect. The passage does not highlight the order of response to an international crisis. Hence, the identification of the first choice is not possible based on the passage alone. Also, the passage is not about international crisis and the role of trade diplomacy, but about the role of soft power. Hence, this option is not correct.

Option (c) is correct. The passage notes, “…smart public diplomacy requires an understanding of the roles of credibility, self-criticism, and civil society in generating soft power.” This understanding of the different roles to generate, and therefore enhance soft power is a multi-faceted approach and can be seen as the essence of the passage. Hence, this option aptly captures the crux of the passage.

Option (d) is incorrect. The passage states, “…soft power is the ability to affect others to obtain the outcomes one wants through attraction and persuasion.” The passage is about soft power and its role in diplomacy. However, this answer option talks about a component of soft power, which is merely a peripheral argument. It is not the crux of the passage. Hence, this option is not correct.

Solution (b)

Explanation: 

New speed = 4/5 of its usual speed

So, New time taken = 5/4 of the usual time

[time = distance/speed, if distance is constant then time ∝ 1/speed ]

So, ( 5/4 of the usual time) – (usual time) = 20 min

⇒ ( 5/4 -1) of the usual time = 20 min

⇒ 1/4 of the usual time = 20 min

⇒ usual time = (4×20) min = 80 min.

Hence, option (b) is the correct answer

Solution (d) 

Explanation: 

Expenditure=10 (number of family members)2 

So E1=10(x)2 

And E2=10(x-1)2 

Now, E1-E2 = 50 

Or 10(x2-(x-1)2) = 50 

Or x2-(x2+1-2x) = 5 

Or 2x-1 = 5 

Or x = 3 

Hence, option (d) is the right answer.  

Solution (c)

Explanation: 

Option (a):

Statements 1, 2 and 3 alone are not sufficient, as we cannot find a link between S and P in these statements.

Option (b):

Statements 1, 3 and 4 alone are not sufficient, as we cannot find a link between S and P in these statements.

Using all the four statements, we get the following family tree:

Hence, option (c) is correct.

Test explained

Test explained