Learn How to Subtract Integers in Five Minutes
Subtracting Integers is Hard!
So here's the deal. Subtracting integers gives a lot of people a really hard time. For some reason, this is a topic that isn't covered very well by most Algebra 1 instructors because it's taken for granted as a skill. When teachers and instructors do take special time out to spend on teaching students how to subtract integers, it usually involves some complicated set of rules that tries to get students to memorize every possible case. This is a very ineffective strategy for teaching students how to subtract integers. There's a better way, and you can learn it here inside of five minutes.
First, we're going to make sure you know how to add integers. There's a short section that will show you how to do this, along with a short quiz to make sure you know what you're doing before you move ahead.
Second, we're going to show you a simple trick for subtracting integers. This is so simple it's ridiculous. There's also a short quiz where you can test out your new skillset for subtracting integers at the end.
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The Official Integer Banner
Can You Add Integers?
Before you can learn to subtract integers using our super secret awesome sauce, you've got to know how to add integers. Adding integers is really easy. There are two cases: if the signs are the same, and if the signs are different.
If the signs are the same, you just add the two numbers together and keep the sign. For example, 3 + 9 = 12, and -4 + -3 = -7. It's like adding 3 apples to 9 apples, or 4 pears to 3 pears. This is pretty simple.
If the signs are different, then you subtract the two numbers and keep the sign of the largest number. So if you had -4 + 7, first you would do 7 - 4 to get 3. Then you'd keep it as a positive 3 since the largest number of 7 or -4 is positive. For another example, to do -8 + 2 you'll subtract 8 - 2 to get 6, and since the larger of the two numbers is negative, your final answer is -6.
You need to make sure that you have this down pat before we look at the easy way to subtract integers. Take this short quiz below to see if you've got this.
Adding Integers Quiz
The Real Secret to Subtracting Integers
This is kind of cheap. Okay, I'll be honest. This is really cheap. If you know how to add integers, then you already know how to subtract integers. The reason why is that you can change a subtraction problem into an addition problem if you change the sign of the second number. Here are some examples.
8 - 4 becomes 8 + -4, and you get 4.
12 - (-3) becomes 12 + 3, and you get 15.
-4 - 6 becomes -4 + -6, and you get -10.
To change a subtraction problem into an addition problem, do the following two steps:
Step 1: Change the - to a +.
Step 2: Change the sign of the second number.
I have absolutely no idea why this isn't taught in every Algebra 1 class in the world because it teaches you how to subtract integers without learning any new skills. Below we've created a short quiz for you to test out your new integer-subtracting skills.