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Video: Finding the Missing Numerator/Denominator in Equivalent Fractions

Kathryn Kingham

Complete the following: 8/15 = 40/_ = _/30.


Video Transcript

Complete the following: eight fifteenths is equal to 40 over blank is equal to blank over 30.

We’ll start with the first set of fractions. Eight fifteenths is equal to 40 over what? First, I noticed that 40 is a multiple of eight. Eight times five is equal to 40. And we remember that, for fractions to remain equal, you must multiply or divide the numerator and the denominator by the same amount.

Since we’re multiplying the numerator by five, eight times five equals 40, we need to multiply the denominator by five. We multiply 15 by five. Five times five is 25. Five times one is five, plus two equals seven. 15 times five equals 75. Our first missing value is 75.

Now we need to find the missing value over 30. If we look at the denominators, I noticed that 30 is 15 times two. 15 times two equals 30. And if we multiply the denominator by two, we multiply the numerator by two. Eight times two equals 16. Our second missing value to make equivalent fractions is 16. Eight fifteenths equals 40 over 75, which is equal to 16 over 30.