Mental Addition of 2-Digit Numbers

Mental Addition of 2-Digit Numbers

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Additions past ten poster

  • To add 2-digit numbers mentally, it is important to know the addition results shown above.

how to do mental addition

  • To add two numbers mentally, add the digits separately.
  • Add the tens digits and then look at the ones digits to decide what the answer ends in.
  • For example in 32 + 29, we add the tens digits first.
  • 3 + 2 = 5.
  • Adding the ones, 2 + 9 = 11.
  • Because 11 ends in a 1, we know our answer ends in a 1.
  • We increase the 5 in the tens column to a 6.
  • 32 + 29 = 61.

Add the tens column and then the ones column separately.

The answer ends in the same digit that the sum of the units column ends in.

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example of mental addition of the 2 digit numbers 36 + 49

  • We first add the tens column digits.
  • 3 + 4 = 7. We hold this number in our head.
  • We now add the digits in the ones column.
  • 6 + 9 = 15.
  • So we add one to the tens column and our answer ends in a 5.
  • The tens column increases from 7 to 8 and the ones column is 5.
  • 36 + 49 = 85.

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Mental Addition of 2-Digit Numbers: Interactive Questions

Mental Addition of 2-Digit Numbers: Interactive Questions

Mental Addition of 2-Digit Numbers Worksheets and Answers

Mental Addition

What is Mental Addition?

Mental addition means to add numbers in your head without writing down any steps or notes as part of the calculation. All of the calculations are done in your head.

There are various strategies for mental addition, however, with each method, it is important to hold values in your head. The fewer the steps, the better the method as it is easier to hold the numbers in your head.

How to do Mental Addition

To do mental addition, use the following steps:

  1. Add the digits in the tens column together and remember this result.
  2. Add the digits in the units column together.
  3. If this result is larger than ten then add one to your tens column answer from before.
  4. The units column of the units column result is the units digit of your answer.

We only hold the result of the tens column in our head while we add the units column.

To add 2-digit numbers, it is first worth knowing the following 1-digit additions:

Additions to 20 list of answers

In this first example, we have 32 + 29.

how to add 32 and 29 mentally by looking at the units

The first step is to add the digits in the tens column.

3 + 2 = 5.

adding 32 and 29 mentally by looking at the tens

The next step is to add the digits in the units column.

2 + 9 = 11

11 is larger than 10 and so, we need to add 1 to our result from adding the tens column. This is because adding 11 is the same as adding ten and then adding 1.

how to add 32 and 29 by adding the units

The 5 in the tens column becomes a 6.

adding the units of 32 and 29 to see that we need to add another ten and our number will end in a 1

Because 11 ends in a 1, we know that our digit in the units column of our answer is also a 1.

how to add 32 and 29 fast mentally

32 + 29 = 61

Quick mental addition of 2 digit numbers example

In this next example we have the mental addition of the 2-digit numbers 44 + 28.

how to add 44 and 28 mentally

The first step to adding two 2-digit numbers mentally is to add the digits in the tens column.

4 + 2 = 6

looking at the tens when we add 44 and 28 mentally

The next step is to add the digits in the units column.

4 + 8 = 12

To add 12, we add 10 and 2.

This means that we increase the tens column by 1 and our answer ends in a 2.

adding 44 and 28, the units tell us to add another ten and the units end in a 2

The 6 increases to a 7.

The answer ends in a 2 because 12 ends in a 2.

how to add 44 and 28 fast mentally

44 + 28 = 72

When teaching mental addition, we recommend trying to hold the first result in your head whilst carrying out the next part of the calculation. When first learning mental addition, start by writing the result a few times until you get the hang of the method.

Once you get better at performing the written method you will find that it is easier to remember the steps and it will be easier to hold numbers in your head.

adding the two digit number 44 + 28 mentally

In this example of mental addition we have 28 + 25.

We will try and speed up our method.

We add the tens:

2 + 2 = 4

Quick Addition 3

8 + 5 = 13 and so, we increase 4 to 5 in the tens column. Our answer ends in 3.

28 + 25 = 53

Here is another example of adding 2-digit numbers mentally.

We have 36 + 49.

Adding the tens digits we have 3 + 4 = 7.

Adding the units digits we have 6 + 9 = 15.

We increase the 7 to an 8 and our answer must end in a 5.

Quick mental addition example of 36 + 49

36 + 49 = 85

In this example of adding mentally, we have 69 + 29.

Adding the tens, 6 + 2 = 8.

Adding the units, 9 + 9 = 18.

Therefore, we increase the 8 in the tens column to a 9 and our answer ends in an 8.

mental addition of 2 digit numbers example of 69 + 29

69 + 29 = 98

With practice, this method is one of the quickest ways to add 2-digit numbers mentally.

When teaching mental addition, if your child struggles with the process, it is worth focusing on writing the steps down until they are mastered. This will make it easier to transfer the process to holding numbers in their head.

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Now try our lesson on 2-Digit Column Addition where we learn how to use the column addition method.