Lesson objective: Solve multiplication problems involving iterating groups and comparisons.

This lesson provides an opportunity for students to apply their knowledge and understanding of the standard algorithm for multiplication to a real-life situation. Students are asked to solve a mystery to determine which employee gets which paycheck when a manager forgets to put names on the checks.

Key Concept students will use:

- The standard algorithm for multiplication works whether the multiplication situation is iterating groups or is a comparison situation.

Skills students will use:

- Use of area models for multiplication; Grade 4 Unit 2; 4.NBT.B.5
- Use of array models for multiplication; Grade 4 Unit 2; 4.NBT.B.5
- Decomposing numbers to find a product; Grade 4 Unit 2; 4.NBT.B.5
- Use of standard algorithm for multiplication; Grade 5, Unit 2; 5.NBT.B.5

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they use clues to make sense of mathematical situations and find solution strategies.

**Key vocabulary: **

- comparison problems
- iterating groups problems
- standard algorithm

**Special materials needed:**

- list of clues
- chart for keeping track of answers