Represent Division of Unit Fractions by Whole Numbers

10 min

Narrative

The purpose of this Estimation Exploration is for students to think about dividing a unit fraction into smaller pieces. In the lesson, students will be given extra information so they can determine the exact size of shaded regions like the one presented here. 

Launch

  • Groups of 2
  • Display the image.
  • “What is an estimate that’s too high? Too low? About right?”
  • 1 minute: quiet think time
Teacher Instructions
  • “Discuss your thinking with your partner.”
  • 1 minute: partner discussion
  • Record responses.

Student Task

How much is shaded?

Diagram. 4 equal sized parts. About 1 fifth of 1 part shaded. Total length, 1.

Record an estimate that is:

too low about right too high

Sample Response

Sample responses:
  • too low: 1100\frac {1}{100} to 140\frac {1}{40}
  • about right: 120\frac {1}{20} to 116\frac {1}{16}
  • too high: 18\frac {1}{8} to 112\frac {1}{12}
Activity Synthesis (Teacher Notes)
  • Draw and display the image:
    Diagram
  • “How is this diagram the same as the diagram in the problem? How is it different?” (Both diagrams show 14\frac{1}{4} of the whole and then a piece of that 14\frac{1}{4} is shaded. The shaded piece in this diagram is cut horizontally. The other diagram is long and narrow and the shaded piece is an entire vertical slice.)
Standards
Building Toward
  • 5.NF.7.a·Interpret division of a unit fraction by a non-zero whole number, and compute such quotients. <em>For example, create a story context for (1/3) ÷ 4, and use a visual fraction model to show the quotient. Use the relationship between multiplication and division to explain that (1/3) ÷ 4 = 1/12 because (1/12) × 4 = 1/3.</em>
  • 5.NF.B.7.a·Interpret division of a unit fraction by a non-zero whole number, and compute such quotients. <span>For example, create a story context for <span class="math">\((1/3) \div 4\)</span>, and use a visual fraction model to show the quotient. Use the relationship between multiplication and division to explain that <span class="math">\((1/3) \div 4 = 1/12~\)</span> because <span class="math">\((1/12) \times 4 = 1/3\)</span>.</span>

10 min

15 min

10 min