Ask someone to mix these Mental Logs number sticks up in any combination. Can you figure out the total in your head more quickly than they can add the numbers on a calculator? Yes. In fact, you can probably tell them the total faster than it takes them to enter the first number. How does this math magic trick work?

Mathematician Dr. Katie Steckles demonstrates a simple mental math trick in this Numberphile video: Number Sticks. Buy the Mental Logs magic trick on Amazon, or make your own. How long can you confound your friends, family, and classroom before they figure out how it works?

Follow this with the Universal Calendar Puzzle: Figure out the day of the week for any date ever and how to multiply numbers by drawing lines.And previously: Fold & Cut Theorem – Cut any shape from only one cut.