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Mental Subtraction - Grade 3




 


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

In these lessons, we will learn how to describe and apply mental mathematics strategies for subtracting two 2-digit numerals, such as:

  • subtracting and compensating
  • use addition to subtract
  • subtraction using doubles


Subtracting and Compensating

In this method, we take the subtrahend (second number) to the nearest multiple of ten, subtract and then compensate to get the answer.

Example:
69 − 28 =
28 is close to 30
69 − 30 = 39
39 + 2 more
So, 39 + 2 = 41


How to subtract in your head using a technique called compensation.



This is a tutorial about Using Compensation to Subtract Whole Numbers.





Use Addition to Subtract

In this method, we think in terms of addition and use addition to subtract.

Example:
To determine the difference between 62 and 45,
Think:
5 more than 45 will get me to 50, 10 more is 60
I`ve added 15 so far and 2 more is 62, so my difference is 17.


Think Addition, Story problems and subtraction.


Subtraction using Doubles

Use a doubles fact you know, to help find the difference.

Example:
62 – 30=
30 + 30 = 60
60 – 30 = 30
32 is 2 more than 30
So 62 – 30 = 32

Subtracting Doubles and Near Doubles
Using Doubles and Building on Doubles is a mental math strategy that introduces students to the concept that the addition doubles and near doubles can be used for subtraction as well.

This video outlines the basic ideas behind using doubles and building on doubles.




 

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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