Videos, solutions, examples, worksheets, games and activities to help Grade 3 students learn mental addition strategies.

In these lessons, we will learn how to describe and apply mental mathematics strategies for adding two 2-digit numerals, such as:
• adding from left to right (partial sums algorithm).
Related Topics: Addition by Making 10

### Adding from left to right

Add the tens and add the ones and then combine them together.
Example:
46 + 12 =
40 + 10 = 50
6 + 2 = 8
50 + 8 = 58
So, 46 + 12 = 58
This is also called the partial sums algorithm.

How to add two-digit numbers by adding from left to right or partial sums algorithm?
Example:
34 + 23
Partial Sums Strategy for adding Two Digit Numbers
Example:
46 + 36

Taking one addend to the nearest multiple of 10 and then compensating
Example:
69 + 28 =
69 is close to 70
70 + 28 = 98
69 + 28 is 1 less
So, 69 + 28 = 97

Examples:
How would you use compensating to solve these problems?
34 + 49
29 + 66
53 + 28
36 + 41
21 + 35
45 + 16
34 + 25
Examples:
55 + 19
120 + 61

Use a doubles fact you know to help find the sum.
Example:
32 + 30 =
30 + 30 = 60
32 + 30 is 2 more
So 32 + 30 = 62