Students use their knowledge of multiplication and division with whole numbers and with fractions to multiply and divide with decimals, and apply this understanding to the context of measurement conversion.
Math
Unit 6
5th Grade
In Unit 6, 5th grade students use their procedural knowledge of multiplication and division with whole numbers, combined with their newly acquired understanding of multiplication and division with fractions, to multiply and divide with decimals, reasoning about the placement of the decimal point. They then apply this to the context of word problems, including those involving measurement conversion.
In 4th grade, students were first introduced to decimal notation for fractions and reasoned about their size (4.NF.5—7). Then, in the first unit of 5th grade, students developed a deeper understanding of decimals as an extension of our place value system, understanding that the relationships of adjacent units apply to decimal numbers, as well (5.NBT.1), and using that understanding to compare, round, and represent decimals in various forms (5.NBT.2—4). Next, students learned to multiply and divide multi-digit whole numbers in Unit 2 (5.NBT.5—6), skills upon which decimal computations will rely. In Unit 4, students explored the other two operations with decimals not addressed in this unit: addition and subtraction (5.NBT.7). In Unit 5, students learned to multiply and divide with fractions, including relating fractions to the operation of division; multiplying a fraction by a fraction, including mixed numbers; and dividing a unit fraction by a whole number and vice versa (5.NF.3—7), which will help them make sense of analogous cases of decimal multiplication and division. Thus, this unit is dependent on a lot of prior learning, both in 4th grade and 5th grade.
This unit starts with multiplying a decimal by a single-digit whole number, then multiplying a decimal by a multi-digit whole number, and finally multiplying a decimal by another decimal. Then, students progress to dividing a decimal by a single-digit whole number, then dividing a decimal by a two-digit whole number, and finally solving cases involving decimal divisors. Throughout these topics, students use the same methods to compute decimal products and quotients as they did for whole-number products and quotients, but they must reason about the placement of the decimal point. It is only in the last lesson of each topic that students generalize the pattern of the placement of the decimal point. The various lines of reasoning, and their advantages and disadvantages, can be read on pages 19 and 20 of the NBT Progression linked in the “Unit-Specific Intellectual Preparation” section. Students also solve myriad word problems as well as write and solve expressions involving decimals as a way to support the major work (5.OA.1, 5.OA.2). Finally, the unit closes with students learning to convert among different-sized standard measurement units within a given measurement system and solve word problems that use those conversions (5.MD.1), which extends the work from 4th Grade Math of converting from a larger unit of measurement to a smaller one (4.MD.1—2). As noted in the Progressions, “this is an excellent opportunity to reinforce notions of place value for whole numbers and decimals, and the connection between fractions and decimals (e.g., $$2\tfrac{1}{2}$$ meters can be expressed as 2.5 meters or 250 centimeters)” (GM Progression, p. 26), as well as computations with these types of numbers (5.NBT.7, 5.NF), thus connecting the work of unit conversion with major work of the grade.
Reasoning about the placement of the decimal point affords students many opportunities to engage in mathematical practice, such as constructing viable arguments and critiquing the reasoning of others (MP.3) and looking for and expressing regularity in repeated reasoning (MP.8). For example, “students can summarize the results of their reasoning as specific numerical patterns and then as one general overall pattern such as ‘the number of decimal places in the product is the sum of the number of decimal places in each factor’” (NBT Progression, p. 20).
In 6th Grade Math, students will become fluent with all decimals computations that they’ve developed in 5th grade (6.NS.3). In 7th Grade Math, students will also learn that every fraction can be represented with a decimal that either terminates or repeats. Then in 8th Grade Math, students learn that terminating and repeating decimals are rational numbers and that there are numbers that are irrational whose decimal expansion does not repeat. Then, students use the work they start in this unit in 8th grade in the context of scientific notation. Thus, this unit has many interesting connections and applications for many years to come.
Pacing: 27 instructional days (24 lessons, 2 flex days, 1 assessment day)
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The following assessments accompany Unit 6.
Have students complete the Pre-Unit Assessment and Pre-Unit Student Self-Assessment before starting the unit. Use the Pre-Unit Assessment Analysis Guide to identify gaps in foundational understanding and map out a plan for learning acceleration throughout the unit.
Have students complete the Mid-Unit Assessment after lesson 16.
Use the resources below to assess student understanding of the unit content and action plan for future units.
Before you teach this unit, unpack the standards, big ideas, and connections to prior and future content through our guided intellectual preparation process. Each Unit Launch includes a series of short videos, targeted readings, and opportunities for action planning to ensure you're prepared to support every student.
Area model for multiplication | |
Partial products algorithm | |
Standard algorithm for multiplication | |
Area model for division | |
Partial quotients algorithm |
conversion factor
To see all the vocabulary for Unit 6, view our 5th Grade Vocabulary Glossary.
Topic A: Multiplying Decimals
Topic B: Dividing Decimals
Topic C: Decimal Expressions and Real-World Problems
Topic D: Measurement Conversion and Real-World Problems
Key
Major Cluster
Supporting Cluster
Additional Cluster
CCSS.MATH.PRACTICE.MP1 — Make sense of problems and persevere in solving them.
CCSS.MATH.PRACTICE.MP2 — Reason abstractly and quantitatively.
CCSS.MATH.PRACTICE.MP3 — Construct viable arguments and critique the reasoning of others.
CCSS.MATH.PRACTICE.MP4 — Model with mathematics.
CCSS.MATH.PRACTICE.MP5 — Use appropriate tools strategically.
CCSS.MATH.PRACTICE.MP6 — Attend to precision.
CCSS.MATH.PRACTICE.MP7 — Look for and make use of structure.
CCSS.MATH.PRACTICE.MP8 — Look for and express regularity in repeated reasoning.
Unit 5
Multiplication and Division of Fractions
Unit 7
Patterns and the Coordinate Plane
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