Harvey Mudd College invited me to a Mathemagics show, put on by one of its math professors. It was pretty cool, and I learned how to square two-digit numbers in my head. I will share my knowledge with the world!

Pick a number- let’s use 47.

1. Add numbers to 47 to make it end in a zero. Two-digit numbers ending in zero are easy to multiply. So we’ve added 3 to 47 to make 50.
2. Subtract from your original number the number you just added to it. 47 - 3 = 44.
3. Multiply 44 and 50 in your head. This is the hardest part. In this case, we get 2200.
4. Square the number you added to and subtracted from your original number. In this case, it’s 3² = 9.
5. Add the number you just got (9) to the number you got last time (2200). You get 2209, and that’s 47²!

It’s really easier than it seems.