Here's a question for you:
A bat and a ball cost $1.10. The bat costs $1.00 more than the ball.
How much does the ball cost?
Did the answer 10 cents immediately spring to mind? It certainly did me for me when I first attempted to solve this puzzle and I confidently predict that 10 cents would be the answer offered by the vast majority of your students were you to present them with the puzzle in class.
Of course, once you take the time to reflect on the fact that the difference between $1.00 and 10 cents is only 90 cents, then it becomes obvious that the 10 cents answer is wrong and the correct answer is actually 5 cents.
The Bat cost: $1.05
The Ball cost: $0.05
This 'simple' but ingenious puzzle was devised by Shane Frederickas part of a 3-item Cognitive Reflection Test (CRT), which he developed to help illuminate his research into cognitive ability. The brilliant thing about the bat and ball puzzle is that to arrive at the correct solution (which is easily understood when explained) requires as Frederick states:
The suppression of an erroneous answer that springs "impulsively" to mind.
Most notably addressed by Nobel Prize winning psychologist Daniel Kahnemanin his book 'Thinking, Fast and Slow', the idea that we draw upon two distinct types of cognitive processes, i.e., those employed quickly with very little thought and significantly slower processes which require much more conscious deliberation is an enduring and engaging topic within psychology.
The Cognitive Reflection Test provides a great way for psychology instructors to explore 'fast' and 'slow' thinking with their students. It also provides a solid foundation from which to examine other cognitive topics such as decision making and IQ.
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