# 10 Little Hacks From Math Nerds That I Tried And Memorized Because They're So Easy And Useful

Recently, I asked the BuzzFeed Community for their best math trick. I'm not talking quantum physics here, but just, you know, an easy way to figure out how much butter I need if I'm doubling a recipe. The answers are remarkably useful, so without further ado, here they are!

1."Sales! If something is 70% off, you are paying 30%. If something is \$150 on sale for 70% off rather than figure out 10% and multiply by 7 and subtract that from \$150."

2.Find the area of an equal-sided shape by multiplying the center an edge, the length of one side, and half the amount of sides.

3."Very small and is just a parlor trick, but if you multiply any double-digit number by 11, then you just add the two numbers of the double-digit together and put that in the middle."

4."The one that a lot of people find helpful, especially if you cook or bake a decent bit, is the following: multiplying fractions is no problem--top times top (numerator multiplied by numerator) over bottom times bottom (denominator multiplied by denominator)."

5.Divisibility rules are wildly useful.

6."Percent can be tricky, especially if you don’t have a calculator, BUT, they’re 'reversible' (not proper math term)."

7."To divide by 5 in your head, double the number, then move the decimal point once to the left (divide by 10)"

8."When I add, I break it down and do easy first, then hard. So for 25 + 56, I do 25 + 50 = 75 + 6 = 81"

9."The nines multiplication hand trick!"

10."It’s easier to add numbers that end in 0, so kind of a different take on another comment...This especially helps with mental math. You could even take it a next step by saying 39 is “1” away from 40. So instead of adding 73+39, you add 70+40, which is 110, then subtract the “1” and get the final answer of 109."

Do you have a math tip you swear by? Tell us all about it in the comments below!