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5th grade · Math · Unit 13 of 14

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.

Alaska content standards learning standard: 5.NF.1; 5.NF.2 · adding and subtracting fractions and mixed numbers with unlike denominators, including in word problems

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 Alaska

In the Alaska content standards, this is unit 13 of 14 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: Alaska Department of Education and Early Development

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 1/2 − 1/5?

    1/2 − 1/5 = ?

    • 7/10
    • 2/5
    • 0
    • 3/10

  2. Question 2

    Is 1/2 + 5/8 more or less than 1?

    • Exactly 1
    • More than 1
    • Less than 1

  3. Question 3

    Amir walks 1/6 mile to the park and then 1/3 mile to the library. How far is that in all?

    • 1/2 mile
    • 2/9 mile
    • 1/4 mile
    • 5/9 mile

  4. Question 4

    What is 1/3 + 3/5?

    1/3 + 3/5 = ?

    • 1
    • 14/15
    • 4/15
    • 1/2

  5. Question 5

    What is 2 3/4 + 1 1/6?

    • 3 2/5
    • 3 11/12
    • 4 11/12
    • 2 11/12

  6. Question 6

    What is 4/5 − 1/3?

    4/5 − 1/3 = ?

    • 8/15
    • 1/5
    • 7/15
    • 3/2

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