Addition Equations with Two-Digit Integers

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  • 0:02 Addition Equations
  • 0:59 Finding X
  • 2:25 Example 1
  • 2:59 Example 2
  • 3:25 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 to solve addition equations where you have two digit integers. Learn how subtraction is involved in finding your missing value.

Addition Equations

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?

Finding X

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?

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