Multiplying two numbers whose difference is two.

You can use this trick for calculations such as 11 x 13, 13 x 15, 24 x 26 etc. where the numbers differ by 2.

Square the number between these two numbers and then subtract 1 from the result.

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Cross Multiplication

This is a very powerful trick. You can multiply any 2 digit number by another 2 digit number.

22 x 31 = ?? (Write the multiplicants is the this form)

Multiplying two numbers between 101 to 109

Here the answer will be a five digit number beginning with 1.

Multiplying by Altering

This trick can be used when one of the multiplicants end in 9. The trick is to add 1 to the number that ends in 9 and then multiplying it with the second multiplicant.

Subtract the second multiplicant from the above result.

19 x 5 = ??

Answer 95

329 x 4 = ??

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Have fun with the trick

Answer is 54

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Multiplying by 25

This is applicable when number is completely divisible by 4 .
Multiplying by 25 is child’s play if you know the trick.Divide the number by 4 and multiply by 100.

24 x 25 = ??                                               

Divide 24 by 4
24 ÷ 4 = 6

Multiply 6 by 100
6 x 100 = 600

Answer is 600

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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

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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.

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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.

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Multiplication by 12

The method is called “Doubling & then adding to the neighbor”

This rule has to be remembered whenever we multiply a number by 12.The right most digit has to be doubled and then right most neighboring digit has to be again added. This will be clear with an e.g.

234 x 12 = 2808

Put 0 in the beginning and at the end of number.
02340

• As the original no. is 234 so we start with 4 and not 0.

Double of 4 is 8
8 + 0 (0 is the first neighbor to it’s right) is 8
So the first digit of the answer at the unit place is 8.

• Next we take 3

Double of 3 is 6
6 + 4 is 10 (4 is the first neighbor to it’s right)
So the second digit of the answer is 0 (1 is carried over).

• Next we take 2

Double of 2 is 4
4 + 3 is 7 (3 is the first neighbor to it’s right)
So the third digit of the answer is 8 (7 + 1 (carried forward from the previous step ) = 8 )

• Next we take 0

Double of 0 is 0
0 + 2 is 2 (2 is the first neighbor to it’s right)
So the forth digit of the answer is 2

Therefore  234 x 12 = 2808

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