Multiply More Decimals
10 min
Narrative
The purpose of this Estimation Exploration is for students to apply what they know about area and multiplication of decimals to a situation where the side lengths of the rectangle are decimals. Students will approximate the length and width to obtain a product of decimals which they can find mentally. This prepares them for work in the lesson where students will find more complex products of decimals since making an estimate is a good way to check work.
Launch
- Groups of 2
- Display the image.
- “What is an estimate that’s too high? Too low? About right?”
- 1 minute: quiet think time
Teacher Instructions
- “Discuss your thinking with your partner.”
- 1 minute: partner discussion
- Record responses.
Student Task
Central Park is a large park in Manhattan. It is about 3.85 kilometers long and 0.79 kilometer wide. What is the approximate area of Central Park?
Record an estimate that is:
| too low | about right | too high |
|---|---|---|
Sample Response
Sample responses:
- Too low: 2 to 2.5 square kilometers
- About right: near 3 square kilometers
- Too high: 3.5 square kilometers or more
Activity Synthesis (Teacher Notes)
- Invite students to share their estimates.
- “How do you know the area is greater than 2 square kilometers?” (I know that 3×0.7 is 21 tenths or 2.1 and it’s more than that.)
- “How do you know the area is less than 3.2 square kilometers?” (I know 3.85 is less than 4 and 0.79 is less than 0.8. Then 4×0.8 is 32 tenths or 3.2.)
Standards
- 5.NBT.1·Recognize that in a multi-digit number, a digit in one place represents 10 times as much as it represents in the place to its right and 1/10 of what it represents in the place to its left.
- 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.A.1·Recognize that in a multi-digit number, a digit in one place represents 10 times as much as it represents in the place to its right and 1/10 of what it represents in the place to its left.
- 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.
20 min
15 min
Knowledge Components
All skills for this lesson
No KCs tagged for this lesson
Multiply More Decimals
10 min
Narrative
The purpose of this Estimation Exploration is for students to apply what they know about area and multiplication of decimals to a situation where the side lengths of the rectangle are decimals. Students will approximate the length and width to obtain a product of decimals which they can find mentally. This prepares them for work in the lesson where students will find more complex products of decimals since making an estimate is a good way to check work.
Launch
- Groups of 2
- Display the image.
- “What is an estimate that’s too high? Too low? About right?”
- 1 minute: quiet think time
Teacher Instructions
- “Discuss your thinking with your partner.”
- 1 minute: partner discussion
- Record responses.
Student Task
Central Park is a large park in Manhattan. It is about 3.85 kilometers long and 0.79 kilometer wide. What is the approximate area of Central Park?
Record an estimate that is:
| too low | about right | too high |
|---|---|---|
Sample Response
Sample responses:
- Too low: 2 to 2.5 square kilometers
- About right: near 3 square kilometers
- Too high: 3.5 square kilometers or more
Activity Synthesis (Teacher Notes)
- Invite students to share their estimates.
- “How do you know the area is greater than 2 square kilometers?” (I know that 3×0.7 is 21 tenths or 2.1 and it’s more than that.)
- “How do you know the area is less than 3.2 square kilometers?” (I know 3.85 is less than 4 and 0.79 is less than 0.8. Then 4×0.8 is 32 tenths or 3.2.)
Standards
- 5.NBT.1·Recognize that in a multi-digit number, a digit in one place represents 10 times as much as it represents in the place to its right and 1/10 of what it represents in the place to its left.
- 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.A.1·Recognize that in a multi-digit number, a digit in one place represents 10 times as much as it represents in the place to its right and 1/10 of what it represents in the place to its left.
- 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.