Multiply up to 20 x 20 in your mind.

With this trick, you will be able to multiply any two numbers, from 11 to 19 in your mind quickly, without the use of a calculator.

15 x 13

Always place the larger number of the two on top in your mind. Cover 15 and “3″ from 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 number “3″ and the single digit above it i.e “5″ to get 15 (3 x 5 = 15)

Add 180 + 15 = 195

Time for you to try

Multiplying by 9 or 9’s

Any number can be multiplied by 9 by applying the following rule.

“By one less than the one before” is used here in combination with “Subtract All from 9 and Last From 10″.

763 x 999 = 762237

• 763 is first reduced by 1 (one less than the one before)

763 less 1 is 762. This is the first part of the answer.

• Then apply the rule “subtract all from 9 and the last from 10″ to 763

i.e. 7 and 6 of 763 are subtracted from 9 and last digit 3 of 763 is subtracted from 10.

(9 - 7 = 2 9 - 6 = 3 10 - 3 = 7) we get 237, which is the second part of the answer.

1867 x 99999 = 186698133

Here, as 1867 has 4 digits, and 99999 has 5 digits,

We put a zero in front of 1867 that is 01867.

• This is reduced by 1 (rule - one less than the one before) to get 1866 as the first part of the answer.

Then applying the rule - subtract all from 9 and last from 10 to get 01867 (9 - 0 = 9, 9 - 1 = 8, 9 - 8 = 1, 9 - 6 = 3, 10 – 7 = 3)

We get 98133 as the second part of the answer.

Time for you to try

Want to practice again?

Multiplying by 5

The quick way to multiply a number by 5 is to divide it by 2 and multiplying it by 10.

16 x 5 = ?

Cut 16 to half by dividing it by 2.
16 ÷ 2 = 8

Multiply it by 10
8 x 10 = 80

Answer is 80.

Time for you to try