Endless Worksheets

4th Grade Math · Equivalent Fractions

Missing denominator Worksheets

Fresh practice, ready to print. Answer key included.

Problems such as 2/3 = 8/?. The missing denominator is 12.

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Missing denominator Worksheets: page 1 of a free printable 4th grade math worksheet
Page 1 of a sample worksheet

How it works: a quick refresher

The rules this worksheet practices, then one problem worked from start to finish.

StrategyHow it works
Same multiplierMultiply the numerator and the denominator by the same number. 2/3 = (2 × 4)/(3 × 4) = 8/12.
Same divisorDivide the numerator and the denominator by a common factor. 8/12 = (8 ÷ 4)/(12 ÷ 4) = 2/3.
Why it stays the sameMultiplying the top and the bottom by 4 cuts each piece into 4 and takes 4 times as many. The amount does not change.
Simplest formKeep dividing by a common factor until the only common factor is 1. 6/8 = 3/4.
Tenths and hundredths1/2 = 5/10 = 50/100. The same rule covers decimals written as fractions.

Worked example

Find the missing numerator: 2/3 = ?/12.

  1. 1Ask what 3 was multiplied by to make 12. 3 × 4 = 12.
  2. 2Multiply the numerator by the same number: 2 × 4 = 8.
  3. 32/3 = 8/12.
  4. 4Check by simplifying 8/12. Divide the top and the bottom by 4 to get back to 2/3.

Ready-made versions

Three fixed versions you can link to or share. Each is a PDF with its own answer key.

Grade level and standard

Written for 4th grade math (fractions) and aligned to CCSS 4.NF.A.1. It also works as review in later grades.

Common questions

Is there an answer key?
Yes. Every worksheet has a matching answer key with each answer worked on the same grid or layout as the question. The worksheet code printed at the bottom of each page pairs a sheet with its key.
Is 8/12 wrong if the simplest form is 2/3?
8/12 and 2/3 are the same amount. The missing-number problems ask for the numerator or denominator that makes the denominators match. The simplest-form problems ask for 2/3.
Why can 1/2 be 50/100?
100 is 2 × 50, so multiply the numerator by 50 as well: 1/2 = 50/100. That is the hundredths way to write one half, the same amount as 0.50.
How many different versions are there?
About a million per skill. Each time you press the button the problems are generated fresh, so you can print a different version for every student, a retake, or another night of practice.
Are the worksheets free?
Yes. They are free to print and copy for your home or classroom, with no sign-up.

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