Subtraction By Complement Method

In this method we are using method of complement.

This method is useful for numbers more than three digits.

Let’s understand this method by taking an example.

Ex: 3178 – 2398

Divide these numbers into double columns.

$Description: D:\Site Articles\Subtraction\images\subtraction_by_complement_cr.png$

Here 98 is greater than 78 so we are adding a complement of 98 in 78.

Complement of 98 = 100 – 98 = 2 (Complement of x = 100 – x)

So 78 + 2 = 80

Add ‘–1’ to the carry.

$Description: D:\Site Articles\Subtraction\images\subtraction_by_complement1_cr.png$

Now, 31 – 23 = 8

And 8 – 1(Carry) = 7

$Description: D:\Site Articles\Subtraction\images\subtraction_by_complement2_cr.png$

So the answer is 780.

Let’s take another example.

Ex: 4523 – 2176

Divide these numbers into double column.

$Description: D:\Site Articles\Subtraction\images\subtraction_by_complement3_cr.png$

23 is less than 76 so add complement of 76 in 23.

Complement of 76 = 100 – 76 = 24

So 23 + 24 = 47

And add a carry of ‘–1’.

$Description: D:\Site Articles\Subtraction\images\subtraction_by_complement4_cr.png$

Now 45 – 21 = 24

And 24 – 1(Carry) = 23

$Description: D:\Site Articles\Subtraction\images\subtraction_by_complement5_cr.png$

So the answer is 2347.