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How to Find a Missing Numerator: Lesson for Kids

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  • 0:04 Fractions and Fairness
  • 0:22 Parts of Fractions
  • 0:39 Equivalent Fractions
  • 1:17 Finding 2nd Fraction…
  • 2:26 Finding 1st Fraction…
  • 3:10 Lesson Summary
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Lesson Transcript
Instructor: Mark Boster
Sometimes you need to know if two fractions are equal. But what happens if you don't know what the numerator of one of the fractions is? In this lesson, we'll show you what to do.

Fractions and Fairness

Bobby and Tommy each ask for a cookie. Their mother tells them they can each have one from the cookie jar. Bobby's cookie is a little smaller than Tommy's cookie. 'That's not fair!' Bobby says.

Just like the boys want to be treated fairly and equally, so do fractions. Yes, fractions!

Parts of Fractions

Fractions have two parts to them, separated by a line called the vinculum, sometimes called a fraction bar. The top number of the fraction is called the numerator and tells us how many parts we have. The bottom number is called the denominator and tells us how many parts there are in the total.

Equivalent Fractions

Sometimes, two fractions are worth the same amount. For example, you can see that 2/4 of the box is colored in, which is the same as 1/2.


fractions


Let's look at another example: 3/4 is the same as 6/8. How do you know this to be true? The proof is in the pie chart diagram. The top circle has 3 out of the 4 parts shaded in. The bottom circle has 6 of the 8 parts shaded in. However, both fractions refer to the same part of the circle.

You can check your results by dividing. Here, both the numerator (6) and the denominator (8) are divisible by 2.


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Finding 2nd Fraction Numerators

What would happen if a numerator were missing? Well, if you're given two fractions and told that they are equivalent fractions, you can find the missing numerator using multiplication or division.

In all equivalent fractions, both the numerator and denominator of the first fraction can be multiplied by the same number to get the numerator and denominator of the second fraction.

Say one of the numerators was missing from those pie chart equations:

3 / 4 = x / 8

You can see that there is an x alongside one of the numerators. That represents the number you are trying to find.

The answer lies in discovering what the first denominator can be multiplied by to get the other denominator. You might be good enough at your times tables to know that 4 times 2 is 8. But you can also check this number by dividing the denominator (8) by the denominator (4), which equals 2.

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