Mental Addition - Grade 3

Videos, worksheets, games and acivities to help Grade 3 students learn mental addition strategies.

In this lesson, 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.

Example:
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

Example:
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.

Example:
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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