10 Great Math Tricks to Do Calculations in Your Head

this is a great detailed list of helpful math tricks, most of them I didn't know before.

clipped from listverse.com 10 Easy Arithmetic Tricks clipped from listverse.com 1. The 11 Times Trick We all know the trick when multiplying by ten - add 0 to the end of the number, but did you know there is an equally easy trick for multiplying a two digit number by 11? This is it: Take the original number and imagine a space between the two digits (in this example we will use 52: 5_2 Now add the two numbers together and put them in the middle: 5_(5+2)_2 That is it - you have the answer: 572. If the numbers in the middle add up to a 2 digit number, just insert the second number and add 1 to the first: 9_(9+9)_9 (9+1)_8_9 10_8_9 1089 - It works every time. 2. Quick Square If you need to square a 2 digit number ending in 5, you can do so very easily with this trick. Mulitply the first digit by itself + 1, and put 25 on the end. That is all! 252 = (2x(2+1)) & 25 2 x 3 = 6 625 3. Multiply by 5 Most people memorize the 5 times tables very easily, but when you get in to larger numbers it gets more complex - or does it? This trick is super easy.