Mental Maths

Mental Addition Strategies

What is mental addition?

• Mental addition means to do the addition of numbers in your head mentally without using a pen paper or any machine.
• Mental addition tricks help us to do addition faster and easily.

We will learn some easy methods to do addition fast.

Addition of 1-digit and 2-digit numbers

• Addition by making 10.

  • We use number bonds of 10.
    
  • In the above example, we know that the number bond of
    10 as 7 + 3 = 10
  • So, we take away 3 from 29 and add it to 7.
  • 29 becomes 26. We can split it as 20 + 6.
  • Now adding 10 + 20 + 6, we get 36.

• Addition by splitting

  • Split two-digit numbers into tens and ones.
    
  • In the above example, we can split the number 13 as one 10 and 3 ones.
  • Then we can add 5 + 3 = 8.
  • Now adding this 8 to 10, we get 18.

Addition of 2-digit numbers

• Addition of tens numbers.

  • Add the Tens place numbers only.
    
  • In the above example, Ones place numbers are 0. We know that, 0 + 0 = 0. So, ones place number will be always 0.
  • Then directly add tens place numbers here: 3 + 6 = 9
  • We get sum as: 30 + 60 = 90

• Another method (Count forward by observing tens-place numbers)

  • Between 30 and 60, the number 60 is greater.
  • The number 30 has 3 at its Tens place. So, from 60 count 3 steps forward in the form of tens.
    

• Addition by columns.

  • We add the numbers in the unit place and the numbers in the tens place separately. (Imagine numbers in column.)
    
  • In the above example, first we add Ones place digits. Remember this answer. This answer will be Ones place digit in the final answer.
  • Then add Tens place digits. This answer will be the Tens place digit of our final answer.

  Case 2: When we get sum of ones place digits as a 2-digit number

  • If we get 2-digit number as the sum of ones place digits, add one to the tens column answer.
    
  • In the above example, first we add Ones place digits:
    7 + 6 = 13.
    The number 3 in this 13 is our ones place digit number in the answer and we hold 1.
  • Then we add Tens place digit: 5 + 2 = 7
    We add that 1 to 7: 1 + 7 = 8

• Addition by splitting

  • Split two-digit numbers into tens and ones.
    
  • In the above example, we split the number 23 as: 20 + 3
  • And split the number 14 as 10 + 4
  • Then add 1-digit numbers: 3 + 4 = 7
  • Then it is easy to add: 20 + 10 + 7 = 37

• Addition by rounding off numbers into tens.

  • Here we rounded off one addend.
    
  • In the above example, if we add 3 to 57, we get 60.
  • So, we take away 3 from 38 and added it to 57.
  • 57 became 60 and 38 became 35.
  • By adding 60 and 35, we got 95.