Lesson Plan

Decimal Product Reasonableness

Discuss correct decimal placement using logical arguments and by multiplying whole numbers. Use this lesson as a standalone lesson or use it as support to the lesson Multiply Decimals.
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This lesson can be used as a pre-lesson for the Multiply Decimals lesson plan.
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This lesson can be used as a pre-lesson for the Multiply Decimals lesson plan.



Students will be able to multiply decimals using the standard algorithm and estimating decimal point placement.


Students will be able to explain how they placed the decimal point in decimal products using a place value chart and peer conversations.


(3 minutes)
Standard Algorithm and Decimal PlacementFormative Assessment: Peer Explanations ChecklistVocabulary Cards: Decimal Product ReasonablenessGlossary: Decimal Product ReasonablenessTeach Background Knowledge TemplateWrite Student-Facing Language Objectives Reference
  • Display the expression 33 x 53 and provide a story problem for students to contextualize the expression. For example, "The grocery store received 33 boxes of cereal. Each box had 53 mini boxes of cereal. How many boxes of mini cereal boxes did the grocery store receive?" Ask students to solve the problem on their whiteboards.
  • Tell students to share their answers with partners while you listen to their language use. (Tip: take note of their own language and their ability to solve the multiplication problem to inform the amount of time you spend on review throughout the lesson.)
  • Have a student model solving the problem and show the steps they used to find the product (i.e., 1,749).
  • Explain that students will use their understanding of the standard algorithm with the multiplication of whole numbers to talk about the product of decimals.