Wednesday, November 28, 2007

Multiplication tricks


Here are a couple of multiplication tricks that are pretty cool:


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.


Take any number, then divide it by 2 (in other words, halve the number). If the result is whole, add a 0 at the end. If it is not, ignore the remainder and add a 5 at the end. It works everytime:



  • 2682 x 5 = (2682 / 2) & 5 or 0

  • 2682 / 2 = 1341 (whole number so add 0)

  • 13410

Let’s try another:



  • 5887 x 5

  • 2943.5 (fractional number (ignore remainder, add 5)

  • 29435

Multiply by 11
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.

More math tricks


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1 comment:

Anonymous said...

it's too early for math... besides that's what my calculater's for