# Question Video: Writing an Additional Expression to Find the Missing Number Mathematics • Kindergarten

There are 8 red and green cups. If 2 of them are green, how many red cups are there?

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### Video Transcript

There are eight red and green cups. If two of them are green, how many red cups are there?

This word problem is all about taking apart or breaking up a group of objects into two groups. And the group of objects we’re thinking about is a group of red and green cups. And there are eight of them. Let’s use eight cubes to represent our eight cups. Now we can use the information in the first sentence to label our cubes. We know there are eight red and green cups, so let’s label the whole amount eight.

The next piece of information we’re told is about part of the eight cups. And we’re told that two of them are green. Now again, we can use this piece of information to label our diagram some more. Two out of our eight cubes we know are going to be green. Now we’re asked, how many red cups are there?

Well, because we were told to begin with that there were eight red and green cups and only two of them are green, we know that the rest of the cups must be red. Now again, we can show this in our line of cubes. We don’t know how many there are in this part, but we do know that this is the part we need to find. The whole amount is worth eight, and we need to break apart the whole amount into two parts.

Our first part represents the number of green cubes, and we know that this is two. And the second part represents the number of red cubes that we’ve got. So to find the answer, we need to start with the whole amount, which is eight, and take away or subtract the part that we know already, which is two. This is going to leave us with the part that we don’t know.

So to represent our two green cups, let’s take away two green cubes. One, two. Now, how many cubes do we have left? One, two, three, four, five, six. We’ve broken apart the number eight into a group of two and a group of six. So we can complete our part–whole model with this information. And we can write the answer in our number sentence too. If there are eight red and green cups and two of them are green, we can find out the number of red cups by splitting up or taking apart the number eight into a group of two and then counting what’s left. Eight take away two equals six. And so we know that the number of red cups must be six.