How to Balance Subtraction Equations

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  • 0:01 Subtraction Equations
  • 0:44 A Missing Value
  • 1:29 Finding the Missing Value
  • 2:38 Example
  • 3:18 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

Watch this video lesson to learn how you can find the missing value in a subtraction equation. Learn what it takes to make sure that both sides of a subtraction equation are equal.

Subtraction Equations

In this lesson, we will talk about subtraction equations. A subtraction equation is a mathematical equation that involves the subtraction operator. Specifically, we will talk about those mathematical equations that show two numbers being subtracted being equal to two other numbers being subtracted. Because there is an equal sign in between, both sides must equal the same number. For example, 5 - 3 = 10 - 8 is a subtraction equation in which both sides equal the same thing. 5 - 3 = 2 and 10 - 8 = 2.

It's important to know how to work with these subtraction equations because being able to spot whether both sides of an equation are equal or not is a good skill to have. For example, you may need to use this skill when taking tests and when figuring out problems in the real world.

A Missing Value

When you are taking a test or figuring out a problem in the real world, you won't always be given all the numbers like in the first example. You won't see 5 - 3 = 10 - 8. Instead, you might see 5 - ? = 10 - 8 or even 5 - 3 = ? - 8.

The missing value could be anywhere in your subtraction equation. It is now your job to find the missing value. We call finding the missing value in a subtraction equation balancing our subtraction equation. It's called balancing because after we are done, both sides will be equal.

If you think about two things being weighed on one of those old-time scales where you have two bowls on either side, then you can see how the subtraction equation is balanced once both sides are equal. So, how do you go about balancing a subtraction equation?

Finding the Missing Value

Let's use our critical thinking skills to see if we can figure this thing out. Let's say we need to balance this equation:

45 - ? = 90 - 50

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