August 24, 2015
by Josephine Alston

Lesson plan

Multiplication: Solving for Unknown Factors

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Grade Subject View aligned standards

Students will be able to solve for the unknown factor in multiplication problems.

(10 minutes)
  • Tell your students that today they are going to learn strategies for solving for the unknown factor involving multiplication problems.
  • Ask your students to share division strategies they know.
  • As the students share, list the strategies on the board. Your students might offer suggestions such as repeated subtraction or arrays.
(15 minutes)
  • Write a few multiplication problems on the board with an unknown factor. For example, 6 x ____ = 36.
  • Have your students rewrite the problem as a division problem, as follows: 36 ÷ 6 = _____.
  • Ask your students to choose an effective division strategy that they know.
  • Solve the problem using repeated subtraction: 36-6=30-6=24-6=18-6=12-6=6-6=0.
  • Then, show your students how to solve the problem using arrays or grouping: XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX XXXXXX
  • Explain to your students how you got the answer 6.
(15 minutes)
  • Have your students solve _____ X 5 = 40 using what they think is the most efficient strategy.
  • Ask for volunteers to raise their hands and share with the class the steps to solve the problem.
  • As the problem is being solved aloud, write down the steps on the whiteboard.
  • When the problem is done, review it with the class for accuracy.
(15 minutes)
  • Give the students the Solve the Unknown Factor worksheet to complete.
  • Enrichment: Have your students skip the division step on their papers to solve the multiplication problems. Encourage them to memorize multiplication facts to quickly solve problems.
  • Support: Give your students simpler problems to solve, such as 3 x ___ = 12. Use manipulatives to help show grouping and arrays.
(10 minutes)
  • Walk around and observe the students as they work on completing the assignment.
  • Monitor the students as they work, making sure that the problems are done correctly.
(10 minutes)
  • Ask for volunteers to share their answers and justification.
  • As the problems are reviewed in front of the class, have the students check their answers for accuracy.

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