Introduction to subtraction

[Video title “Introduction to Subtraction” appears] 

Narrator: Welcome to the video in the introduction to subtraction. [Shows a drawing of apples and oranges] So subtraction is just the opposite of addition. In addition we’re combining like things, and in subtraction, we’re separating like things. Notice that both in addition and subtraction, the items that you’re working with have to be the same, or in the same group, or similar in some way. Here’s an example of why.

Suppose we have seven apples [formula appears above the drawings: seven apples minus three oranges], now, take away three oranges, how many apples do you have [Question appears below. “How many apples remain?”. A large red X then appears on the whole screen] Logically, this doesn’t even make any sense [“Does not make sense!!” text box appears]. In order to take something away from the apples, we have to take away apples, cause that’s what we have. We can’t take away oranges if we don’t have them.

[Oranges disappear from the video]

So here’s an example that does make sense. Again, let’s say you have seven apples. Now take away three, we can do that. [“Answer: 4 apples remain”] Now, what we’re left with are four apples. This totally makes sense.

[9 blue cubes appear]

In this example, we have nine. Now, let’s take away four, or subtract four. So we’re starting with nine, and then we pick four to take away. Move those over, what we’re left with is just five. Sometimes when doing subtraction, we need to actually regroup. Which is to take ten to the place value to the left, and then add it to the place value to the right. So in this example we have fourteen. Let’s take away nine. Well we only have four ones and one set of ten, so we can’t take nine ones away from four ones. We only have four. So we need to change this so that we have enough ones to take away nine. We can do this by splitting up our group of ten. Let’s take our group of ten, we’re gonna move it over here with the ones, and split it up. Now we’ve split up our group of tens, and now we have a total of fourteen ones. Now, we can take away nine. Take those away and we’re left with five. One, two, three, four, five. So that’s our answer.

[end of video]