Mental Addition Strategies

We will learn some easy methods to do addition mentally.

Addition of 1-digit numbers

• Addition by counting forward
• Consider the first number and count the number of steps forward as equal to the second number.

Example:



Method

We will start from number 2 and count 5 steps forward.



So, we get:



• Addition by counting forward from a larger number
• Find out the larger number between addends and count forward from that number.

Example:



Method


• If we count from 3, we have to count 6 steps forward but if we count from 6, we have to count 3 steps forward.
• This method will make our addition faster.

So, we get:



• If numbers are the same, do addition by doubling it.
• If addends are the same, double that number.

Example:



Method


• In the above examples, we can easily count a table of given numbers up to 2. (i.e. 4 twos are 8, 3 twos are 6).
• Instead of adding the same number twice, we can multiply that number by 2. It will give the same answer.

So, we get:



• If numbers are close, do addition by double the number.
• If two numbers are close to each other, double the smaller number.

Example:



Method


• In the above example, 8 is close to 6, but 8 is 2 bigger than 6.
• So, first we add 6 + 6. Here we can double the number 6 and make addition easy.
• After getting 6 twos are 12, we can add 2. (Simply count 2 steps forward from 12)
• And we got our answer. This method will make addition faster.

So, we get:



• Adding numbers by making up 10.
• We use number bonds of 10.
• Following are the number bonds of 10.


Example:



Method


• In the above example, we know that adding 8 and 2 will get 10.
• So, we took away 2 from 5, and add it to 8. It will give us 10.
• If we take away 2 from 5, we will get 3.
• Now add 10 and 3, it will give us 13.
• Adding 10 plus 3 is easier than adding 8 plus 5.

So, we get:



• Addition of any number with 9.
• We use the following number bond of 10:

1 and 9 = 10

Example:



Method


• In we have to add any number to 9, just remove 1 from that number and add it to 9.
• We get, 9 + 1 = 10.
• After removing 1 from the given number, it is easy to add the remaining number to 10. (Take the number that comes before number.)

So, we get:

Addition of 1-digit number and 10

• Addition of any 1-digit number with 10.
• We use the fact that if we add any number to 0 we get that same number as answer.

Example:



Method


• In the above example, we have to add Ones place numbers.
• The number 10 has 0 in its Ones place.
• Adding any number to 0 gives us that number itself as an answer.
• So, to add any 1-digit number to 10, just replace the number 0 in 10 with that 1-digit number.

So, we get: