Multiply Up to 20X20 In Your Head

I will assume that you know your multiplication table reasonably well up to 10x10. This trick will extend you up to 20x20 in about FIVE minutes of work! You will be able to multiply any two numbers from 11 to 19 in your head quickly and without the use of a calculator.

Try this example:

• Take 15 x 13 for an example.
• Always place the larger number of the two on top in your mind.
• Then draw the shape of Africa mentally so it covers the 15 and the 3 from the 13 below. Those covered numbers are all you need.
• First add 15 + 3 = 18 add a zero behind it (multiply by 10) to get 180.
• Multiply the covered lower 3 x the single digit above it the "5" (3x5= 15)
• Add 180 + 15 = 195.

That is It! Wasn't that easy? Practice it on paper first! Just to be totally honest: 20x20=400

Here are some practice problems.  Simply click on the button you think has the correct answer.

1) 11 X 10