User:Rayhan/Math shortcuts

Suppose you want to quickly multiply any number with 11, there is an easy way: 352х11 Leave spaces between the first and the last digit: 3 (5) 2   3+5, 5+2 let the first digit stay where it is. Put the sum of the first digit and the middle digit after the first digit: 3(8)  5+2 do the same thing with the middle and last digit:

3(8)  (7)2

The answer is 3872.

Another example: 2645х11 2[ 2+6 6+4 4+5   ]5 =    8  10   9 we cannot put 10 directly, so you have to carry the "1" of 10 should be added to 8. 2[ 8+1 ← 0  9    ]5 2[    9   0  9    ]5  =29095

Ok, this method is more useful for multiplications of smaller units such as the first example, as it saves time.

Contributed by Rayhan