What do you get if you multiply all the numbers on a phone keypad?

How to think about it

1. List the digits on a phone keypad: 1 through 9 in the grid, and 0 at the bottom.
2. Multiplying 1 × 2 × 3 × … × 9 would be tedious, so look for a shortcut before you start.
3. One of the keys is 0, and any product that includes a factor of 0 is 0.
4. The answer is zero, no matter what order you multiply in.

Why “Zero” is the answer

A phone keypad includes the digit 0, and multiplying anything by 0 gives 0, so the whole product collapses to zero. The riddle counts on you picturing only the 3×3 block of digits 1 to 9 and forgetting the bottom row. The star and pound keys are not numbers, so they do not change anything.

Common wrong answers

• 362,880. That is 9 factorial, the product of 1 through 9, which ignores the zero key.
• 45. Forty-five is the sum of 1 through 9, not a product, and it also leaves out the 0.