 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
How to use Near Doubles for addition?
When adding near doubles and one is 1 more, add the two doubles and then 1 more.
When they are apart by two, here is what you need to do. Add the two doubles and then 2 more.

Try the free Mathway calculator and problem solver below to practice various math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.  