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Mental Addition - Grade 3

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.
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

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?
Examples:
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?
Examples:
55 + 19
120 + 61



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?
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.

Rotate to landscape screen format on a mobile phone or small tablet to use the Mathway widget, a free math problem solver that answers your questions with step-by-step explanations.


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


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