[C06] The Cognitive Reflection Test

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 answers are: $0.05, 5 mins, 47 days.

What is interesting about this test is that each of the question has an "intuitive" answer which is actually wrong. To get all questions right, most people would need to suppress their immediate reactions and reflect carefully to come to the correct answers. This is supposed to reflect the capacity for deliberate and reflective reasoning and to avoid jumping to conclusions. Researchers claim that the short test actually provides a rather good measurement of rational thinking and cognitive ability.

In case you are wondering about how well other people do, here are the average scores for students at various US universities:

• Massachusetts Institute of Technology: 2.18
• Princeton: 1.63
• Harvard: 1.43
• Michigan State: 0.79

Don't worry if you did not get all the answers right. What is important is to realize that in some situations, spending more time thinking about the question is better than coming up with an answer very quickly!