Addition of 2-Digit Numbers Mentally

Mental math helps children solve addition problems quickly without writing them down. In this lesson, we will learn how to perform the addition of 2-digit numbers mentally using easy strategies, tricks, solved examples, and practice exercises. These methods improve speed, accuracy, and confidence in mathematics.

What is Mental Addition?

Mental addition means adding numbers in your head without using paper, pencil, or calculator.

Example: 24 + 15 = 39

Strategies for Addition of 2-Digit Numbers Mentally:

I: Break Apart Method:

Split numbers into tens and ones.

Example:

   34 + 25

= (30 + 20) + (4 + 5)

= 50 + 9

= 59

II: Make Tens Strategy:

Example:

   38 + 6

= 38 + 2 + 4

= 40 + 4

= 44

III: Compensation Strategy:

Example:

    49 + 33

= 50 + 33 - 1

= 83 - 1

= 82

Solved Examples on Mental Addition:

A: Add the tens. Then add the ones. (in case of addition without carrying)

We check the ones digit of both the addends. If no carrying is required, then we follow the steps given below.

1. Find 24 + 35

Express 35 as the sum of the nearest 10 and remaining ones, that is.

35 = 3 tens 5 ones = 30 + 5

Now,

Step I: Add 3 tens (30) to 24.               24 + 30 = 54

Step II: Add 5 ones (5) to the result.      54 +  5 = 59

             So, 24 + 35 = 59

B: Add the tens. Then subtract the ones. (in case of addition with carrying)

We check the ones digit of both the addends. If carrying is required, then we follow the steps given below.

2. Find 44 + 38

Express 38 as the difference of the nearest ten and the additional ones.

38 = 4 tens - 2 ones

     = 40 - 2

Now,

Step I:   Add 4 tens (40) to 44.                       44 + 40 = 84

Step II: Subtract 2 ones from the result.         84  -   2 = 82

              So, 44 + 38 = 82.

Practice Questions:

1. Add the following mentally:

(i) 23 + 34 = ___

(ii) 45 + 22 = ___

(iii) 57 + 16 = ___

(iv) 61 + 18 = ___

(v) 48 + 25 = ___

Answer:

1. (i) 57

(ii) 67

(iii) 73

(iv) 79

(v) 73

Worksheet on Adding 2-Digit Numbers Mentally

The addition of 2-digit numbers mentally becomes easy when children learn simple mental math strategies like breaking apart numbers and making tens. Regular practice helps students calculate faster and develop strong number sense skills.

FAQs on Addition of 2-Digit Numbers Mentally:

Related Math Lessons:

• Addition of 2-Digit Numbers
• Addition without regrouping
• Addition with Regrouping
• Mental Math Worksheets
• Properties of Addition
• Word Problems on Addition

3rd Grade Math Lessons

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