Math Brain Teasers

Try each puzzle before opening the answer. Many famous teasers are designed so the first answer that pops into your head is wrong; the explanations show the math that gets it right.

How to use these brain teasers

Read the puzzle, write down your first answer, then check it before opening the solution. When you are wrong, reread the explanation and try to state the trap in one sentence.

Why our intuition fails

Puzzles like the bat and ball trigger a fast, automatic answer (10 cents) that feels right. Slowing down and writing an equation, b + (b + 1.00) = 1.10, gives the correct 5 cents. Practicing this habit helps on tests full of tempting wrong choices.

Using them in class

Use one teaser as a warm-up: students answer silently, compare with a partner, then explain. The goal is reasoning out loud, not speed.

Math Brain Teasers quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

Are these brain teasers for kids or adults?

Both. Most need only arithmetic and careful thinking.

Where are the answers?

Under each puzzle: open “Show the answer.”

Are these riddles original?

Some are classic puzzles retold in our own words; all explanations are our own.

How many teasers are there?

24, in logic, numbers, geometry and probability.

Can I use them in my classroom?

Yes, they work well as warm-ups.

Sources

• Frederick (2005), Cognitive Reflection and Decision Making, Journal of Economic Perspectives

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