Estimating Volume: The Money Munchers

Mathematical goals

This lesson unit is intended to help you assess how well students are able to:

  • Model a situation.
  • Make sensible, realistic assumptions and estimates.
    • Use assumptions and estimates to create a chain of reasoning, in order to solve a practical problem.


In this unit, students choose and use mathematics to model a problem situation:

  • Before the lesson, students attempt The Money Munchers task individually. You then review their solutions and create questions for them to answer in order to improve their work.
  • At the start of the lesson, students work individually, answering your questions about the task.
  • Next, students work collaboratively in small groups. Their task is to produce a better solution to The Money Munchers problem than they did individually. Then, in the same small groups, students analyze responses to The Money Munchers task written by students in another class.
  • In a whole-class discussion, students compare and evaluate the solution methods they have seen and used.
  • In a follow-up lesson, students review their individual and joint solutions and write about what they have learned.

Materials required

  • Each student will need a copy of the task sheet The Money Munchers and the How Did You Work? questionnaire.
  • Each small group of students will need a new copy of the task sheet The Money Munchers, a sheet of poster paper, and a copy of the Sample Responses to Discuss.
  • Provide calculators for students who choose to use them.
    • There is a projector resource to support whole-class discussions and to help introduce activities.

Time needed

15 minutes before the lesson, a 1-hour lesson, and 10 minutes in a follow-up lesson. Timings given are approximate and will depend on the needs of your class.