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6th-8th Grade Math: Practice & Review55 chapters | 469 lessons

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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 to solve addition equations where you have two digit integers. Learn how subtraction is involved in finding your missing value.

You and your friend are playing a maze game. This is a maze carved out of a huge corn field. The corn is so high that you can't see above it. The way to get out and win this maze game is to figure out which is the correct route. Each path has a number attached to it. You can find the correct route by solving an addition equation for a missing number. This missing number tells you which route to take.

An **addition equation** is a problem that has two or more numbers or integers added together and equaling another integer. For example, 12 + 11 = 23 is an equation. But for our maze game, we are actually missing an integer. So instead of seeing 12 + 11 = 23, you will see 12 + *x* = 23. An *x* is usually used to represent a missing value. It is then your job to find out what this missing integer is. How do you go about doing that?

To find the missing integer, we need to find out what *x* equals. To solve for *x*, we need to get *x* by itself so that we have an equation where *x* equals an integer. This integer will be our answer. To do this, we can use the subtraction property of equality that tells us that if we subtract the same thing from both sides, our equation will still be the same.

Why do we use this property? Well, in our sample problem, 12 + *x* = 23, in order to make the 12 disappear, we need to subtract it. By subtracting 12 from the left side, we are left with just *x*, which is what we want. The subtraction property of equality then tells us that we also need to subtract the 12 from the other side as well. So we have 12 + *x* - 12 = 23 - 12. This becomes *x* = 11. Is this the right answer?

We can check by plugging this answer back into our problem. We have 12 + 11 = 23. Does 12 + 11 really equal 23? Yes, it does, so our answer is correct! Now that you've found what *x* equals, you can now choose the correct path with the number 23 on it.

Let's look at a couple more examples.

*17 + x = 23*

Here we have a 17 that we have to somehow make disappear. Do you remember how we do this? Yes, we need to subtract the 17. Applying the subtraction property of equality, we subtract the 17 from both sides. We have 17 + *x* - 17 = 23 - 17. This becomes *x* = 6. Our missing integer is 6. This tells you and your friend to choose the route labeled with a 6.

*x + 10 = 55*

We are getting the hang of it now. We see a plus 10 so this means that we subtract 10 from both sides. We have *x* + 10 - 10 = 55 - 10. This gives us an answer of *x* = 45. And we are done! You and your friend now choose the route labeled with a 45.

Let's review what we've learned.

An **addition equation** is a problem that has two or more numbers or integers added together and equaling another integer. If we have an addition equation where we have a missing number, we solve it by subtracting the number that is being added from both sides to find the missing number. The missing number is usually represented by an *x*.

When you have finished this lesson, you should be able to:

- Identify an addition equation
- State the subtraction property of equality
- Solve an addition equation missing an integer

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7 in chapter 11 of the course:

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6th-8th Grade Math: Practice & Review55 chapters | 469 lessons

- Finding the Absolute Value of a Real Number 3:11
- Absolute Value & Opposite Integers 4:23
- Integer Inequalities with Absolute Values 7:51
- How to Compare Integers 4:03
- Adding Positive & Negative Integers 6:30
- Addition Equations with One-Digit Integers 4:17
- Addition Equations with Two-Digit Integers 3:55
- Subtraction Equations with One-Digit Integers 6:21
- Subtraction Equations with Two-Digit Integers 5:35
- How to Simplify Expressions with Integers 5:12
- Dividing Integers: Rules & Terminology 6:03
- Multiplying Integers: Rules & Examples 10:53
- Go to 6th-8th Grade Math: Integers

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