Mental Subtraction Strategies

• Mental math is a skill that helps students to do math in their heads without using paper and pencil.
• Mental Math is useful in school and everyday life.
• It also helps to do calculations faster.

In subtraction,

• The larger number is called the minuend.
• The smaller number is called the subtrahend.
• The resultant number is called the difference.

Method 1:(Add, and subtract)

• Express the subtrahend as the difference of the nearest hundred in a one/two-digit number.
• Then do the subtraction while adding the one/two-digit number with the minuend

Example:

Answer:

Now, 189 = 200 – 11

So, 278 – 200 + 11 = 78 + 11 = 89

Method 2:(Split the Problems)

• The basic idea is to split the minuend and subtrahend into two or more numbers which are easier to work with.
• While splitting we will obviously take one number which is nearest to the hundred.

Example:

Answer:

1. 568 = (500 + 68)

         329 = (300 + 29)

         Now, 500 – 300 = 200

         68 – 29 = 39

         So, 200 + 39 = 239

        Hence, 568 – 329 = 239

   b. 

Method 3:(Nikhilam rule)

• Nikhilam rule says that “All from 9 and the last from 10.”
• That means all digits should be subtracted from 9 and the last digit should be subtracted from 10.
• After the subtraction, the difference should be added to the minuend.
• Deleting the left first digit of the sum of the minuend and the result, we get the final result of the subtraction.

Example:

Answer:

1. We need to subtract 123 from 9910 like the following way

      b. 897 – 250 =

          We need to subtract 250 from 9100 like the below way