Lesson plan

7. Convert measurements in order to compare amounts (C)

teaches Common Core State Standards CCSS.Math.Content.4.MD.A.2 http://corestandards.org/Math/Content/4/MD/A/2
teaches Common Core State Standards CCSS.Math.Practice.MP5 http://corestandards.org/Math/Practice/MP5
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Lesson objective: Understand that when solving measurement problems, it sometimes makes sense to convert a larger unit to a smaller unit.

Students bring prior knowledge of using multiplicative comparison to convert units of length, mass, volume, and time from 4.MD.A.1. This prior knowledge is extended to compare quantites that have been converted to the same unit as students show how many times greater one quantity is compared to another. A conceptual challenge students may encounter is recognizing when conversions need to be made and what unit(s) will work. 

The concept is developed through work with measurement tools, function tables, and tape diagrams, which show the number of smaller units that make up a larger unit and then how many times greater one quantity is when compared to another.

This work helps students deepen their understanding of equivalence because a larger unit is equivalent to a certain number of smaller units; therefore, the same amount can be represented by different units.

Students engage in Mathematical Practice 5 (use appropriate tools strategically) as they decide which models show how quantities compare in size to each other and demonstrate the multiplicative relationship between units of measure.

Key vocabulary:

  • capacity
  • conversion
  • cup
  • gallon
  • ounces
  • pint
  • pounds
  • quart
  • unit of measurement

Special materials needed:

  • conversion chart
  • measuring cups