5 useful math tricks

 1.Multiplying by 6

If you multiply 6 by an even number, the answer will end with the same digit. The number in the ten's place will be half of the number in the one's place.

Example: 6 x 4 = 24.


2. The Answer Is 2

Think of a number.

Multiply it by 3.

Add 6.

Divide this number by 3.

Subtract the number from Step 1 from the answer in Step 4.

The answer is 2.

3.Same Three-Digit Number

Think of any three-digit number in which each of the digits is the same. Examples include 333, 666, 777, and 999.

Add up the digits.

Divide the three-digit number by the answer in Step 2.

The answer is 37.


4.Six Digits Become Three

Take any three-digit number and write it twice to make a six-digit number. Examples include 371371 or 552552.

Divide the number by 7.

Divide it by 11.

Divide it by 13.

The order in which you do the division is unimportant!


The answer is the three-digit number.


Examples: 371371 gives you 371 or 552552 gives you 552.


A related trick is to take any three-digit number.

Multiply it by 7, 11, and 13.

The result will be a six-digit number that repeats the three-digit number.


Example: 456 becomes 456456.


5. The 11 Rule

This is a quick way to multiply two-digit numbers by 11 in your head.


Separate the two digits in your mind.

Add the two digits together.

Place the number from Step 2 between the two digits. If the number from Step 2 is greater than 9, put the one's digit in the space and carry the ten's digit.

Examples: 72 x 11 = 792.


57 x 11 = 5 _ 7, but 5 + 7 = 12, so put 2 in the space and add the 1 to the 5 to get 627.

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