Answer these three questions quickly. They are quite simple!

1. 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?

2. If it takes 5 machines 5 minutes to make 5 widgets, how long would it take 100 machines to make 100 widgets?

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

The Cognitive Reflection Test is a short psychological test designed by Shane Frederick at MIT. The test measures a person’s tendency to override an initial “gut” response that is incorrect, and to engage in further reflection to find a correct answer.

CRT also has high correlation with other measures of intelligence, such as the IQ tests. Read the complete text given at the bottom of the article but before that, have a look at the answers.

Answers:

(1) 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?

The answer is 5 cents (not 10).

Bat = Ball + 1.00

Bat + Ball = 1.10

Ball + 1.00 + Ball = 1.10

2Ball = 0.10

Ball = 5 cents!

(2) If it takes 5 machines 5 minutes to make 5 widgets, how long would it take 100 machines to make 100 widgets?

The answer is 5 minutes (not 100).

Ratio:

5 widgets / 5 machines*5 minutes = 1/5

100 widgets / 100 machines*x minutes = 1/5

Hence, 5 minutes!

(3) In a lake, there is a patch of lily pads. Every day, the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long would it take for the patch to cover half of the lake?

The answer is 47 days (not 24).

Every day, the patch doubles in size. So if on nth day the area covered is x, then on (n-1) day, the area covered will be x/2.

Since on 48th day, the entire lake gets covered, on 47th day, 50% of the lake will be covered on 47th day!

Reference:

Shane Frederick’s paper on Cognitive Reflection and Decision Making – Complete text