Using Decimals in a Shopping Context
10 min
Teacher Prep
Setup
Narrative
This activity allows students to review decimal work in a money context. It also offers insights into how students find sums, differences, products, and quotients of decimals. Both questions allow multiple paths of reasoning, including whether to calculate precisely or to estimate.
Monitor for the ways in which students add, subtract, multiply, and divide decimals, as well as how they make estimates. Do they round the cents to the closest dollar, or do they look only at the dollar value to the left of the decimal point? (For instance, some students may round $1.85 to $2.00 because it is the closest whole dollar. Others may round it to $1.00 because “1” is the dollar amount in front of the decimal point.) As students work, select those who use different strategies, and ask them to share during discussions. Note any misconceptions so that they can be addressed later.
Launch
Ask students to name some supplies that the class would need if it was holding a class party. Tell students that this Warm-up is about Clare buying paper plates, napkins, and disposable table covers. Consider reading aloud (or inviting a student to read aloud) the first paragraph in the task statement.
Give students 2–3 minutes of quiet work time, and follow with a whole-class discussion.
Student Task
Clare went to a store that sells a pack of paper plates for $3.25, a pack of napkins for $1.85, and disposable table covers for $0.99 each. She bought at least one of each item and spent no more than $10.
- Could Clare have purchased 2 packs of paper plates, 2 packs of napkins, and 2 table covers? Explain your reasoning.
- Could she have bought 1 pack of paper plates, 1 pack of napkins, and 5 table covers? Explain your reasoning.
Sample Response
- No. Sample reasoning: One pack of paper plates, one pack of napkins, and one table cover cost about $6. So two of each would cost twice this much, about $12.
- No. Sample reasoning: One pack of paper plates and one pack of napkins cost $5.10. Five table covers cost $4.95. Buying these items would cost 5 cents more than $10.
Activity Synthesis (Teacher Notes)
Ask selected students to share their responses and reasoning. Record and display (for all to see) their strategies for adding, subtracting, multiplying, and dividing decimals , including strategies that involve estimation.
To involve more students in the conversation, consider asking some of the following questions:
- “Who can restate ’s reasoning in a different way?”
- “Did anyone solve the problem the same way but would explain it differently?”
- “Did anyone solve the problem in a different way?”
- “Does anyone want to add on to ’s strategy?”
- “Do you agree or disagree? Why?”
Tell students that, in this unit, they’ll continue to solve problems that involve finding the sum, difference, product, or quotient of decimals.
Standards
- 5.NBT.7·Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.
- 5.NBT.B.7·Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.
25 min
Knowledge Components
All skills for this lesson
No KCs tagged for this lesson
Using Decimals in a Shopping Context
10 min
Teacher Prep
Setup
Narrative
This activity allows students to review decimal work in a money context. It also offers insights into how students find sums, differences, products, and quotients of decimals. Both questions allow multiple paths of reasoning, including whether to calculate precisely or to estimate.
Monitor for the ways in which students add, subtract, multiply, and divide decimals, as well as how they make estimates. Do they round the cents to the closest dollar, or do they look only at the dollar value to the left of the decimal point? (For instance, some students may round $1.85 to $2.00 because it is the closest whole dollar. Others may round it to $1.00 because “1” is the dollar amount in front of the decimal point.) As students work, select those who use different strategies, and ask them to share during discussions. Note any misconceptions so that they can be addressed later.
Launch
Ask students to name some supplies that the class would need if it was holding a class party. Tell students that this Warm-up is about Clare buying paper plates, napkins, and disposable table covers. Consider reading aloud (or inviting a student to read aloud) the first paragraph in the task statement.
Give students 2–3 minutes of quiet work time, and follow with a whole-class discussion.
Student Task
Clare went to a store that sells a pack of paper plates for $3.25, a pack of napkins for $1.85, and disposable table covers for $0.99 each. She bought at least one of each item and spent no more than $10.
- Could Clare have purchased 2 packs of paper plates, 2 packs of napkins, and 2 table covers? Explain your reasoning.
- Could she have bought 1 pack of paper plates, 1 pack of napkins, and 5 table covers? Explain your reasoning.
Sample Response
- No. Sample reasoning: One pack of paper plates, one pack of napkins, and one table cover cost about $6. So two of each would cost twice this much, about $12.
- No. Sample reasoning: One pack of paper plates and one pack of napkins cost $5.10. Five table covers cost $4.95. Buying these items would cost 5 cents more than $10.
Activity Synthesis (Teacher Notes)
Ask selected students to share their responses and reasoning. Record and display (for all to see) their strategies for adding, subtracting, multiplying, and dividing decimals , including strategies that involve estimation.
To involve more students in the conversation, consider asking some of the following questions:
- “Who can restate ’s reasoning in a different way?”
- “Did anyone solve the problem the same way but would explain it differently?”
- “Did anyone solve the problem in a different way?”
- “Does anyone want to add on to ’s strategy?”
- “Do you agree or disagree? Why?”
Tell students that, in this unit, they’ll continue to solve problems that involve finding the sum, difference, product, or quotient of decimals.
Standards
- 5.NBT.7·Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.
- 5.NBT.B.7·Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.