Logical Reasoning & Quantitative Techniques Flashcards

Two pipes can fill a tank in 20 and 30 minutes respectively. A drain can empty it in 15 minutes. If all three are open together, in how many minutes will the tank be filled?

Answer: The tank will never fill.

Net rate = 1/20 + 1/30 − 1/15 = 3/60 + 2/60 − 4/60 = 1/60 − 0 = −1/60, which is negative, so the drain empties faster than the pipes fill and the tank never fills.

Argument: 'Speed limits should be abolished because experienced drivers can judge safe speeds.' Which assumption underlies this argument?

Answer: Experienced drivers' judgment is always reliable and sufficient for safety.

The argument assumes experienced drivers' judgment is a reliable and sufficient substitute for standardized speed limits.

If Monday is the 15th of a month and the month has 31 days, on what day does the last day of the month fall?

Answer: Sunday

From the 15th (Monday) to the 31st is 16 days; 16 mod 7 = 2, so two days after Monday = Wednesday — wait: 15+16=31, 16 days later; Monday + 16 = Monday+2 weeks+2 days = Wednesday.

A passage states: 'Eyewitness testimony is often unreliable due to memory distortions.' Which conclusion is best supported?

Answer: Eyewitness testimony should be corroborated with additional evidence before being relied upon.

The passage supports caution about eyewitness testimony, suggesting corroboration is prudent, not that it should be categorically excluded.

Statements: All laws are rules. Some rules are guidelines. Conclusion I: Some laws are guidelines. Conclusion II: All guidelines are laws.

Answer: Neither I nor II follows.

We cannot determine whether the laws that are also rules overlap with the rules that are guidelines, so neither conclusion necessarily follows.

A person invests ₹10,000 at 10% simple interest per annum. After how many years will the total amount be ₹15,000?

Answer: 5 years

Interest needed = ₹5,000; using SI = P×R×T/100, T = 5000×100/(10000×10) = 5 years.

Which pattern of reasoning best describes: 'In all observed cases, contracts signed under duress were held voidable. Therefore, contracts signed under duress are always voidable.'

Answer: Inductive reasoning

Drawing a general rule from repeated specific observations is inductive reasoning.