One puzzle at a time

Challenges

Small problems that look obvious and aren’t. Take a swing at each one — then watch the idea it hides come apart, step by step.

Newest challenge

x + y = 10 and xy = 21. What is x² + y²?

Core

x + y = 10, x y = 21 x^{2} + y^{2} = ?

Topic

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x + y = 10, x y = 21 x^{2} + y^{2} = ?

out 30 mph ⟷ back 60 mph

552 = 92% \times ?

\frac{84 !}{82 ! + 83 !}

6 \div \frac{1}{6} \times 2

b^{3} = b

3% of 4%