Logical Reasoning & Problem Solving Flashcards

A farmer has both chickens and cows. He counts 20 heads and 56 legs. How many cows does he have?

Answer: 8

Let c = cows: 4c + 2(20−c) = 56 → 2c = 16 → c = 8.

Which of the following represents an inductive argument?

Answer: The sun rose every day this week, so the sun will rise tomorrow.

Inductive reasoning draws a probable general conclusion from specific observed instances.

Four people must cross a bridge at night with one torch. The bridge holds only 2 at a time. Their crossing times are 1, 2, 5, and 10 minutes. What is the minimum total time?

Answer: 17 minutes

The optimal strategy (1&2 cross; 1 returns; 5&10 cross; 2 returns; 1&2 cross) takes 17 minutes.

A number is divisible by 9 if:

Answer: The sum of its digits is divisible by 9

The divisibility rule for 9 states that a number is divisible by 9 if and only if the sum of its digits is divisible by 9.

In a logic puzzle, statements A and B cannot both be true, and at least one must be true. If A is false, what is B?

Answer: True

Since at least one must be true and A is false, B must be true.

A car depreciates by 15% per year. If it is worth $20,000 now, what is its approximate value after 2 years?

Answer: $14,450

$20,000 × 0.85 × 0.85 = $20,000 × 0.7225 = $14,450.

Which argument contains the fallacy of 'false dilemma'?

Answer: You must be either with us or against us — there is no middle ground.

A false dilemma presents only two options as if no other possibilities exist, when in fact there may be many.