Mensa IQ Critical Thinking and Problem Solving Flashcards

A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost?

Answer: $0.05

If the ball costs x, then the bat costs x + $1.00, and together they equal $1.10, so 2x = $0.10 and x = $0.05.

If it takes 5 machines 5 minutes to make 5 widgets, how long does it take 100 machines to make 100 widgets?

Answer: 5 minutes

Each machine makes 1 widget in 5 minutes, so 100 machines working simultaneously still take only 5 minutes to produce 100 widgets.

In a lake, a patch of lily pads doubles in size every day. If it takes 48 days for the patch to cover the entire lake, how long does it take to cover half the lake?

Answer: 47 days

Since the patch doubles each day, on day 47 the lake is exactly half covered, and it doubles to full coverage on day 48.

A farmer has 17 sheep. All but 9 die. How many sheep are left?

Answer: 9

The phrase 'all but 9' means all except 9, so exactly 9 sheep remain alive.

A house has four walls, each facing south. A bear walks by. What color is the bear?

Answer: White

The only point on Earth where all four walls of a building can face south is the North Pole, where only white polar bears live.

Three boxes are mislabeled: one holds only apples, one holds only oranges, one holds both. You may pick one fruit from one box. From which box should you pick to correctly label all three?

Answer: The box labeled 'Both'

Since all labels are wrong, the box labeled 'Both' must contain only apples or only oranges; one pick reveals its true contents, and logic determines the rest.

How many months of the year have 28 days?

Answer: 12

All 12 months have at least 28 days — the question asks which months 'have' 28 days, not which have exactly 28 days.