Math

A glass tank holds 28 heads in total — some centipedes (100 legs each), some toads (4 legs each). There are 832 legs. How many toads are there?

Which is a better deal: 20% off followed by an extra 10% off, or a flat 30% off?

A father is 4 times as old as his son. In 20 years, he’ll be only twice as old. How old are they now?

Without a calculator: what is 2 + 2 × 2 ?

A brick weighs 1 kg plus half a brick. How much does the brick weigh?

A standard chessboard has 64 small squares. But how many squares ARE on the board when you count every size?

According to legend, a king promised to give the inventor of chess any reward he asked for. The inventor asked for one grain of rice on the first square, doubling on each next square. How much rice did he actually claim?

Pi Day is celebrated on March 14 (3.14). What’s Pi Approximation Day — and when?

The square root of −1 is called what?

How many prime numbers exist?