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:
Now add the two numbers together and put them in the middle:
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:
1089 - It works every time.