Notice the answer that arrives at once
Some questions hand you an answer in under a second. That answer is often the one the wording invites, not the one the wording states.
So do two things. Notice the fast answer and hold it. Then write the two quantities the question names and check that your answer fits both of them.
1Notice the answer that arrives instantly.
2Write down the two quantities the question names.
3Test the fast answer against both before you commit.
The bat and the ball
A bat and a ball cost $1.10 together. The bat costs $1.00 more than the ball. How much does the ball cost?
The fast answer is 10 cents. Check it: a 10 cent ball makes a $1.00 bat, the total is $1.10, but the gap is only 90 cents, not $1.00.
Take the $1.00 gap out of $1.10 and split the remaining 10 cents in two. The ball costs 5 cents and the bat costs $1.05.
This item was published by Frederick (2005), who used it to show how often a fast answer goes unchecked.
Try one yourself
A ruler and an eraser cost $2.20 together. The ruler costs $2.00 more than the eraser.
Notice your first answer, then check it: does it leave a gap of exactly $2.00?
Try it
How much does the eraser cost?
- 20 cents
- 10 cents
Show the answer
10 cents
Taking the $2.00 gap out of $2.20 leaves 20 cents to share, so the eraser is 10 cents and the ruler is $2.10. The gap is exactly $2.00 and the total is exactly $2.20.
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