Video: Evaluating Unit Fractions of a Quantity

>Fill in the blank: 1/4 of 20 = _.

02:26

Video Transcript

Fill in the blank: one-quarter of 20 equals what.

In the picture, we can see a group of 20 cakes. And to answer the problem, we need to find a fraction of this quantity. We need to find one-quarter of 20. What do we know about the fraction one-quarter? Well, firstly, the numerator is one. This means it’s what we call a unit fraction. In other words, we only need to find one-quarter. We don’t need to find two-quarters or three-quarters, only one. And the bottom number or the denominator in one-quarter is a four. This tells us that we need to split the whole amount into four equal parts. That’s what a quarter is; it’s one out of four equal parts. So to find out what one-quarter of 20 is, we’re going to have to split up 20 into four equal parts.

Now, there are two ways we could do this. Firstly, we could think about the number 20 itself, and we could work out the answer to 20 divided by four. Or we could use the picture of the cakes to help. We could divide this into four equal groups. Let’s try both ways, and if we get the same answer, we know we’ve got it right. Now there’s a quick way we can split things into four. We start by finding a half, and then if we find half again, that gives us four equal parts. We know that half of 20 is 10 and then half of 10 is five. There are four fives in 20. 20 divided by four equals five. It looks like one-quarter of 20 is five, but let’s just check using the picture.

First, we can split the group in half. Now, if we split each half in half by going down the middle, we can see we’re going to end up with some half cupcakes, which we don’t really want. It makes it a bit more tricky to count. So let’s just split each half in half by drawing lines across. There we go. We’ve split the whole amount into four equal groups, and there are one, two, three, four, five cupcakes in each group. We were right. One-quarter of 20 equals five.

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