Lesson Video: Nonunit Fractions Mathematics • 3rd Grade

In this video, we will learn how to model and write nonunit fractions and describe the numbers in the fraction with the words “numerator” and “denominator.”

11:34

Video Transcript

Nonunit Fractions

In this video, we will learn how to model and write nonunit fractions and describe the numbers in the fraction with the words numerator and denominator.

Each of these bar models shows a different fraction. Each of our three bar models have been divided into equal parts. How many equal parts? Let’s count, one, two, three. When we divide a shape into three equal parts, we call each of the parts a third. One of the thirds in this bar model has been shaded orange. So we would say the fraction of this shape which has been shaded is one-third.

How do we write one-third? First, we can write the denominator. This is the number at the bottom of the fraction. The denominator is the number of equal parts, and the numerator or the number at the top of the fraction is a one. This is the number of parts which have been shaded. Two-thirds of our second shape have been shaded, so the denominator is the same. There are still three equal parts. But this fraction has a different numerator because the number of parts which have been shaded is two. If the numerator in a fraction is a one, we call this a unit fraction. The unit means one out of all the equal parts, and nonunit fractions have a numerator greater than one like two-thirds. In this video, we’re learning all about nonunit fractions. Three-thirds of this bar model have been shaded. Three-thirds is equal to the whole amount.

What fraction of these bar models have been shaded? How many equal parts do each of these bar models have? One, two, three, four, five. When we divide a shape into five equal parts, we call each part a fifth. Because we know that each of these models has been divided into fifths, we know they all have the same denominator. This is the number at the bottom of the fraction. The denominator is the number of equal parts we’ve divided our shape into.

Now we just need to write the numerators or the top number on the fraction. The numerator is the number of parts we’ve shaded. The first fraction has two parts out of five equal parts shaded. So we would write this as two-fifths. Three-fifths of our second shape have been shaded and four-fifths of our third shape. When the numerator or the top number in the fraction is greater than one, we call these nonunit fractions.

This is a nonunit fraction. What fraction of this shape has been shaded? There are three equal parts, so each part is a third. Two of our equal parts are shaded, so two-thirds of this shape is shaded. How do we write this as a fraction? The bottom number of the fraction or the denominator tells us the number of equal parts, and in this case there are three. And the numerator or the number on top of the faction tells us how many of our equal parts have been shaded, two-thirds. Let’s practice what we’ve learned about nonunit fractions by answering some questions now.

What fraction is shaded?

In this question, we have to write what fraction of the circle has been shaded. Let’s start by thinking about the denominator or the number on the bottom of the fraction. The denominator is the number of equal parts our circle has been divided into: one, two, three, four, five, six. When we divide a shape into six equal parts, we call each part a sixth. Now we can write the numerator or the top number of our fraction. The numerator is the number of parts which have been shaded. Five out of six equal parts have been shaded or five-sixths. The fraction of the shape which is shaded is five-sixths.

What fraction is shaded?

In this question, we’re given a shape. Some of the shape has been shaded green. We have to write this as a fraction. First, we need to think about the denominator. This is the number that we write at the bottom of the faction. The denominator is the number of equal parts that our shape has been divided into: one, two, three, four, five. When we divide a shape into five equal parts, we call each part a fifth. Now we just need to write the numerator or the number of parts which have been shaded. Two out of the five equal parts are green, so two-fifths of the shape is shaded.

Jackson has shaded part of this whole. Fill in the blank: what parts out of five are shaded. What fraction is shaded?

In this question, we’re shown a model and we can see that Jackson has shaded part of the whole. In the first part of the question, we have to write the number of parts out of the five equal parts Jackson has shaded. We know the whole amount shows five equal parts. Jackson has shaded three of them orange, so we can say that three parts out of five are shaded.

In the second part of the question, we have to write this as a fraction. The bottom number in a fraction is called the denominator. This tells us the number of equal parts our shape has been divided into. We know there are five equal parts. And when we divide a shape into five equal parts, we call each part a fifth. And we know the numerator or the number on top is a three because Jackson has shaded three out of the five equal parts. So the missing number is three. Three parts out of five are shaded. Three out of five equal parts is equal to three-fifths.

Emma has shaded part of this whole. Fill in the blanks: what out of what equal parts are shaded. What fraction is shaded?

In this question, we’re told that Emma has shaded part of this whole. The whole means the whole shape. In the first part of the question, we have to fill in the missing numbers. And we have to write the number of parts which are shaded out of the number of equal parts altogether. Did you count the number of shaded parts? There are four. Four parts of this shape have been shaded blue. How many equal parts has this shape been divided into? Let’s just keep on counting. We counted the four shaded parts. Here’s another part; that makes five, six. Four out of six equal parts are shaded.

How do we write this as a fraction? The numerator or the number on the top is the number of shaded parts. And the number on the bottom or the denominator tells us how many equal parts there are. When we divide a shape into six equal parts, we call each part a sixth, so the fraction of the shape that is shaded is four-sixths.

Write a fraction that has two as the numerator and five as the denominator.

When we write fractions, the number on the bottom is called the denominator. This tells us the number of equal parts that the shape or the number has been divided into. And we’re told that the denominator in this fraction is a five. When we divide a shape into five equal parts, we call each part a fifth. Now that we’ve written the denominator in our fraction, we just need to write the top number, the numerator. We’re told that our faction has a two as the numerator. We could model this by shading two of our five equal parts. If a fraction has two as the numerator and five as the denominator, then the fraction is two-fifths.

What have we learned in this video? We have learned how to model and write nonunit fractions. We have also learned to describe fractions using the words denominator and numerator.

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