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5th grade · Math · Unit 11 of 12

Unlike Denominators

Add fractions with different bottoms

What your child practices

Adding and subtracting fractions and mixed numbers with different denominators by finding a common denominator, and checking with benchmark fractions.

Minnesota K-12 Academic Standards benchmark: 5.3.5.11; 5.3.5.13 · adding and subtracting fractions and mixed numbers with unlike denominators

How we explain it

Children can open this short lesson before they practice.

  1. Find a common denominator.
  2. Rename each fraction with that denominator.
  3. Add or subtract the tops. Keep the bottom. Simplify.

Example: What is 1/2 + 1/3? Common denominator: 6. 1/2 = 3/6 and 1/3 = 2/6. 3/6 + 2/6 = 5/6. Answer: 5/6

Unlike Denominators in Minnesota

In the Minnesota K-12 Academic Standards, this is unit 11 of 12 in 5th grade Math, after Multiply & Divide Fractions and before Volume of Boxes.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Minnesota Department of Education (MDE)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    What is 4/5 − 7/10?

    4/5 − 7/10 = ?

    • 3/25
    • 1/10
    • 3/5
    • 3/50

  2. Question 2

    What is 4 1/5 + 4 1/2?

    • 8 7/10
    • 7 7/10
    • 8 2/7
    • 9 7/10

  3. Question 3

    What is 1/2 + 1/12?

    1/2 + 1/12 = ?

    • 1/7
    • 5/8
    • 7/12
    • 1/12

  4. Question 4

    Maya walks 1/4 mile to the park and then 1/2 mile to the library. How far is that in all?

    • 3/4 mile
    • 7/8 mile
    • 1/3 mile
    • 3/8 mile

  5. Question 5

    Is 5/6 + 1/2 more or less than 1?

    • Exactly 1
    • Less than 1
    • More than 1

  6. Question 6

    What is 2/3 − 3/5?

    2/3 − 3/5 = ?

    • 1/15
    • 1/2
    • 19/15
    • 2/15

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