clipped from: listverse.com   
clipped from: listverse.com   

Galoisfieldlib


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.