Weekend Investigation

10 min

Narrative

The purpose of this Number Talk is to elicit the strategies and understandings students have for fraction multiplication. The whole number 60 is intentionally selected to represent the minutes in one hour. These understandings help students develop fluency and will be helpful later in this lesson when students will need to interpret the number of minutes as fractional parts of one hour.

Launch

  • Display the first expression.
  • “Give me a signal when you have an answer and can explain how you got it.”

  • 1 minute: quiet think time.

Teacher Instructions
  • Record students’ answers and strategies.
  • Keep the expressions and the work displayed.
  • Repeat with each expression.

Student Task

Find the value of each expression mentally.

  • 14×60\frac{1}{4}\times60
  • 34×60\frac{3}{4}\times60
  • 54×60\frac{5}{4}\times60
  • 94×60\frac{9}{4}\times60

Sample Response

  • 15: 60÷4=1560\div4 = 15
  • 45: 3×15=453\times15 = 45
  • 75: 5×15=755\times15=75
  • 135: Add all of the products from the earlier expressions. 15+45=6015+45=60, 60+75=13560+75=135
Activity Synthesis (Teacher Notes)
  • “What is 18×60?\frac{1}{8}\times60? How do you know?” (7127\frac{1}{2}, because that is half of 15. 18\frac{1}{8} is half of 14\frac{1}{4}.)
Standards
Addressing
  • 5.NF.4·Apply and extend previous understandings of multiplication to multiply a fraction or whole number by a fraction.
  • 5.NF.B.4·Apply and extend previous understandings of multiplication to multiply a fraction or whole number by a fraction.

20 min

20 min