Videos, 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.
This video shows how to add two-digit numbers by adding from left to right or partial sums algorithm.
Partial Sums Strategy for adding Two Digit Numbers
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.
This tutorial will show you how to use the compensation strategy to help you to solve addition problems.
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.
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