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College Algebra: Help and Review27 chapters | 228 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.

Subtraction is one of the basic operations in math. Watch this video lesson to learn how you can view and understand subtraction so that you can easily perform it.

So, first, what is subtraction? **Subtraction** is the taking away of a number from another number. We only have one math symbol for this operation, and it is the one that looks like a dash (-). So, if we see a problem such as 4 - 3, we read it as four minus three. The symbol is telling us to take away the second number from the first number.

A good way to view this operation is to think about money. You can think of the minus sign as you having to pay someone back. The first number is the amount that you have on hand, and the second number is the number that you have to pay back.

Alternately, if we view it in terms of the number line, our first number tells us our starting point, and the second number tells us how many spaces to move to the left. Subtraction moves us to the left on the number line. Let's see how this works with an example.

Let's go ahead and subtract 4 - 3. Thinking about this in terms of money, I see that I currently have 4 bucks in my hand. I bump into a friend who bought me lunch the other day, and I have to pay back 3 bucks.

How many bucks do I have left? I'm left with 1 dollar in hand. So, 4 - 3 = 1. We can also view this on the number line. Our starting point is 4. The subtraction of 3 tells us to move three spots to the left. So, I count, 3, 2, and 1. So, 1 is my answer.

What if the number we are subtracting is larger than our beginning number? If we think of it in terms of money, we could be owing money then. So, our answer would have a negative sign in front telling us that we owe.

For example, 8 - 12 has us owing 4 bucks since we only have 8 bucks in hand. We pay back the 8, but we still need to pay back 4 more to get to 12. So, our answer is 8 - 12 = -4. On the number line, if we start at 8 and count 12 steps to the left, we see that we cross 0 and enter the negative numbers. Our end point is -4.

If we had a problem such as 8 - 3 - 2, we remain calm and we just tell ourselves to work from the left to the right. Just like if you were reading, you read one word at a time. In math, we subtract two numbers at a time.

We first subtract our two numbers, the 8 and the 3. What do we get? We get 5. We can then subtract the next number from this answer. So, 5 - 2 gets us to 3. So, that is our answer.

Now, let's review. We have just learned how to **subtract**, the taking away of one number from another. In math, the symbol is a dash (-). We can think of it in terms of money when we owe somebody money, or we can think of it in terms of moving to the left on the number line.

You choose the method that helps you understand the concept of subtraction better. If we are subtracting more than two numbers at a time, we just work our way from the left to the right two numbers at a time.

We first subtract the two numbers to get an answer. Then we subtract the next number from this answer. And we keep going until we've subtracted the last number. The single number that we are left with is our answer.

You will have the ability to do the following after watching this video lesson:

- Define subtraction and identify its mathematical symbol
- Explain how to subtract numbers and how you can use money or a number line as an example to understand subtraction
- Recall the steps involved when subtracting more than two numbers at a time

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College Algebra: Help and Review27 chapters | 228 lessons

- What Is a Number Line? 5:16
- Binary and Non-Binary Operations 5:34
- How to Perform Addition: Steps & Examples 4:07
- How to Perform Subtraction: Steps & Examples 3:46
- How to Multiply Large Numbers: Steps and Examples 7:43
- How to Perform Division: Steps & Examples 3:56
- Performing Long Division with Large Numbers: Steps and Examples 9:12
- Arithmetic Calculations with Signed Numbers 5:21
- The Commutative Property: Definition and Examples 3:53
- The Associative Property: Definition and Examples 4:28
- The Multiplication Property of Zero: Definition & Examples 2:40
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- How to Find the Least Common Multiple 5:37
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