# 5. Using the standard algorithm with iterating groups and comparisons (C)

teaches Common Core State Standards CCSS.Math.Content.5.NBT.B.5 http://corestandards.org/Math/Content/5/NBT/B/5
teaches Common Core State Standards CCSS.Math.Practice.MP1 http://corestandards.org/Math/Practice/MP1
teaches Common Core State Standards CCSS.Math.Practice.MP8 http://corestandards.org/Math/Practice/MP8

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Lesson objective: Understand that the standard algorithm for multiplication is a valid method for solving both iterating groups and comparison problems.

Students bring prior knowledge of the standard algorithm for multiplication from 5.NBT.B.5. This prior knowledge is extended to solving word problems as students solve real-world problems involving iterating groups and/or comparisons. A conceptual challenge students may encounter is identifying problems as either iterating groups, comparisons, or both.

The concept is developed through work with a word problem, which requires students to solve both an iterating group problem and a comparison problem.

This work helps students deepen their understanding of operations because students learn to identify the two mathematics situations and learn that the standard algorithm is an efficient method for solving both problem types.

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they use the standard algorithm for multiplication to solve two different types of multiplication problems.

Key vocabulary:

• comparison problem
• iterating groups problem
• standard algorithm

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