Multiplication by 9

9 is a magic number. We have studied some amazing properties of 9 in previous sections.

Here we are going to see another amazing property of 9, that makes multiplication of any number by 9 very simple.

The rule is when you multiply any number with 9, then the left part of the answer is the result of operation of “original number – number formed by ignoring the one’s place digit – 1”, and the right part is the one’s place digit of the result of multiplication of one’s place digit of original number with 9.

Let us understand this rule with an example:

45 x 9 = ?

There are 2 parts of the answer: Right part or RHS and Left part or LHS.

Left part is: Number – number formed by ignoring one’s place digit – 1, i.e

45 – 4 – 1 = 40 (here we ignore one’s place digit in 45 which is 5)

Right part is: one’s place digit of 45, i.e. 5 x 9 = (4) 5

So, the answer is 40 5.

Let us consider another example.

387 x 9 = ?

This rule can be extended to the multiplication of any number with 9.

Let us practice more:

a. 87 x 9                                 b. 567 x 9

c. 6789 x 9                             d. 45678 x 9

 

⇐ Multiplying by 5, 50, 25

Multiplication by 11 ⇒