Amazing Math Tricks They Didn't Teach You In School
Want to learn how to calculate percentages in your head? Did you know that you can subtract by adding? These math tricks aren't magic, but they certainly seem like it.
Add Large Numbers Quickly
No need for pen and paper when you know this handy shortcut.
Determine Percentages Without a Calculator
Easily calculate tax, tips, and discounts in your head.
Subtract Numbers with a Little Addition
You could use subtraction, or you could go the old-fashioned adding-machine route.
Key Facts In This Video
You can use the "subtract-by-adding" trick with all positive numbers. (0:46)
Old adding machines subtract through the "subtract-by-adding" method. (1:31)
Computers use a binary version of the "subtract-by-adding" method. (2:32)
Fool Your Friends With This Mathematics Trick
You'll look like you're psychic, but really you're just good with numbers.