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).
- addition using compensation
- addition using doubles.
Related Topics: Addition by Making 10
Adding from left to right
Add the tens and add the ones and then combine them together.
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?
34 + 23
Partial Sums Strategy for adding Two Digit Numbers
46 + 36
Addition using Compensation
Taking one addend to the nearest multiple of 10 and then compensating
69 + 28 =
69 is close to 70
70 + 28 = 98
69 + 28 is 1 less
So, 69 + 28 = 97
How to add in your head using a technique called compensation?
How would you use compensating to solve these problems?
34 + 49
29 + 66
53 + 28
36 + 41
21 + 35
45 + 16
34 + 25
How to use the compensation strategy to help you to solve addition problems?
55 + 19
120 + 61
Addition using Doubles
Use a doubles fact you know to help find the sum.
32 + 30 =
30 + 30 = 60
32 + 30 is 2 more
So 32 + 30 = 62
Adding Doubles +1
Doubles and Near Doubles (Addition strategy)
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.
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