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Discovery Education: Math and Economics - Proportions in Money Exchange

Example Web Site and/or Technical Equipment Required


Website Example:

Tech Product Equipment

Computer(s), Internet access

Activity Description

In this lesson students will:

  • research the history of money and share presentations
  • solve problems of proportions using the Rule of Three and the Inverse Rule of Three.
  • convert American and foreign currencies.


  1. Make sure that the site is not blocked at your school
  2. Select the Web Site Example (above) to open the lesson plan.
  3. Review objectives, materials, procedures, evaluation, and vocabulary tabs on top of the lesson plan page.
  4. You may want to modify the lesson in order to meet your students’ needs.


  1. Ask students to research the history of money. Use the sites suggested in the lesson plan.
  2. Let students share their results in a one-page report.
  3. Ask students to pick a partner and share the results with their partners.
  4. Each group of two should report to the class at least 3 interesting facts about the history of money.
  5. Show students examples of proportions. Solve them using the Rule of Three.
  6. Allow time for the students to practice.
  7. Ask students to look online for currency exchange rates. Use sites suggested in the lesson plan.
  8. Choose three different currencies and practice changing dollars into these currencies and the other way around. Use the Rule of Three to find the answer.

Teacher Tips

If you want to go further, you may want to teach how to calculate problems of limiting value using the formula S = Penas. This is the last step in the lesson plan.

More Ways

  • Review the vocabulary list and definitions. The words are important in math and economics.
  • Try some of the other lesson plans offered at this site.

Select subjects and subcategories


  • Algebra
  • Consumer Math
  • Geometry


Social Studies

  • Economics
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OTAN activities are funded by contract CN200091-A2 from the Adult Education Office, in the Career & College Transition Division, California Department of Education, with funds provided through Federal P.L., 105-220, Section 223. However, OTAN content does not necessarily reflect the position of that department or the U.S. Department of Education.