# 11. Identify unit lengths as invariant (C)

teaches Common Core State Standards CCSS.Math.Content.5.MD.A.1 http://corestandards.org/Math/Content/5/MD/A/1
teaches Common Core State Standards CCSS.Math.Practice.MP2 http://corestandards.org/Math/Practice/MP2

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Lesson objective: Understand that measurement of length can be expressed with different unit sizes because we can convert from larger to smaller units by using multiplication.

Students bring prior knowledge of the multiplication of decimals from 4.NBT.A.1. This prior knowledge is extended to the use of multiplication of decimals in making metric conversions as students convert measurements of lengths of cord using various units to the same unit. A conceptual challenge students may encounter is forgetting to put in the unit label, such as cm, mm, or m.

The concept is developed through work with a measurement chart, which is related to the Base-10 Place Value system.

This work helps students deepen their understanding of equivalence because when we convert between measurement units, the length of the item remains the same.

Students engage in Mathematical Practice 2 (Reason abstractly and quantitatively) as they make sense of how metric measurement units compare, such as 10 mm = 1 cm, 100 cm = 1 m, 1000 m = 1 km.  Students will make sense of quantities and their relationships in problem situations by converting between various metric units when measuring length.

Key vocabulary:

• equivalent
• length
• measurement
• metric abbreviations (km, hm, dam, m, dm, cm, mm)
• metric prefixes (kilo-, hecto-, deka-, deci-, centi-, milli-)

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