Use decimal grids or area models to find each product.

Name

Class

Date

Multiplying Decimals

Modeling

Essential question: How do you multiply decimals?

MCC6.NS.3

1 EXPLORE

Modeling Decimal Multiplication

Use decimal grids or area models to find each product.

A 0.3 ? 0.5

0.3

Shade 3 columns of the grid to represent 0.3.

Shade

rows of the grid to represent 0.5. 0.5

The shadings overlap

square(s).

This represents

hundredth(s), or 0.15.

0.3 ? 0.5 =

B 3.2 ? 2.1

3.2

Each row contains 3 wholes + 2 tenths.

Each column contains

whole(s) +

The entire area model represents

tenth(s).

2.1

whole(s) +

tenth(s) +

hundredth(s).

3.2 ? 2.1 =

2-1

video tutor

TRY THIS! 1a. Use the grid to multiply 0.3 ? 0.8.

1b. Draw an area model to multiply 2.2 ? 4.3.

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0.3 ? 0.8 = Module 2

2.2 ? 4.3 = 21

Lesson 1

REFLECT 1c. How are the products 2.1 ? 3.2 and 21 ? 32 alike? How are they different?

To multiply decimals, first multiply as you would with whole numbers. Then place the decimal point in the product. The number of decimal places in the product equals the sum of the number of decimal places in the factors.

MCC6.NS.3

2 E X A M P L E Multiplying Decimals

Dwight bought 2.4 pounds of grapes. The grapes cost $1.95 per pound. What was the total cost of Dwight's grapes?

1.95

? 2.4 780

+ 3900 4.680

2 decimal places + decimal place(s)

decimal place(s)

The grapes cost $

.

TRY THIS!

Multiply. 2a.

12.6

? 15.3 378

+

decimal place(s) decimal place(s)

2b. 9.76

? 0.46

+

decimal place(s) decimal place(s)

+ +

decimal place(s)

decimal place(s)

REFLECT

2c. How can you use estimation to check that you have placed the decimal point correctly in your product?

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Module 2

22

Lesson 1

MCC6.NS.3

3 E X A M P L E Multiplying Decimals

A tree grows 9.25 inches per year. If the tree continues to grow at this rate, how much will the tree grow in 3.75 years?

9.25 decimal place(s)

? 3.75 + 4625 64750

decimal place(s)

+

decimal place(s)

The tree will grow

inches in 3.75 years.

Estimate to check whether your answer is reasonable:

Round 9.25 to the nearest whole number.

Round 3.75 to the nearest whole number.

Multiply the whole numbers.

Is the answer reasonable? Explain.

TRY THIS!

Multiply.

3a. 7.14 ? 6.78 5712

3b. 11.49 ? 8.27

+

+

3c. Rico bicycles at an average speed of 15.5 miles per hour.

What distance will Rico bicycle in 2.5 hours?

miles

3d. Use estimation to show that your answer to 3c is reasonable.

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REFLECT

3e. Compare the products 6.95 ? 38.3 and 69.5 ? 3.83. What do you notice? Explain.

Module 2

23

Lesson 1

pra c t i c e

1. Use the grid to multiply 0.4 ? 0.7.

2. Draw an area model to multiply 1.1 ? 2.4.

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0.4 ? 0.7 = Place the decimal point in each product.

3. 3.9 ? 4.6 = 1 7 9 4

1.1 ? 2.4 = 4. 0.219 ? 6.2 = 1 3 5 7 8

5. 14.9 ? 0.092 = 1 3 7 0 8

6. 5.546 ? 8.14 = 4 5 1 4 4 4 4

Multiply. 7. 0.18 ? 0.06 =

8. 35.15 ? 3.7 =

9. 0.96 ? 0.12 =

10. 62.19 ? 32.5 =

11. 3.4 ? 4.37 =

12. 3.762 ? 0.66 =

13. 11.89 ? 41 =

14. 73.8 ? 19.85 =

15. 12.7 ? 1.83 =

16. 44.1 ? 24.66 =

17. Chan Hee bought 3.4 pounds of coffee that cost $6.95 per pound. How much did he spend on coffee?

$

18. Adita earns $9.40 per hour working at an animal shelter. How much money will she earn for 18.5 hours of work?

$ Catherine tracked her gas purchases for one month.

19. How much did Catherine spend on gas in week 2?

$

20. How much more did she spend in week 4 than in week 1?

$

Week 1 Week 2 Week 3 Week 4

Gallons

10.4 11.5 9.72 10.6

Cost per gallon ($)

2.65 2.54 2.75 2.70

Module 2

24

Lesson 1

Name

Class

Date

2-1

Name ________________________________________ Date __________________ Class__________________

ALEdSSOdN iDteiocimnaalsl Practice 4 Practice B: Multiplying Decimals

Find each product.

1.

0.7 0.3

2.

0.05 0.4

3.

8.0 0.02

________________________

4.

3.5 0.2

_______________________

5.

12.1 0.01

________________________

6.

9.0 0.9

________________________

7. 0.04 ? 0.58

_______________________

8. 2.15 ? 1.5

________________________

9. 1.73 ? 0.8

________________________

10. 6.017 ? 2.0

________________________

_______________________

11. 3.96 ? 0.4

_______________________

________________________

12. 0.7 ? 0.009

________________________

Evaluate 8x for each value of x.

13. x 0.5

14. x 2.3

________________________

16. x 3.12

_______________________

17. x 0.587

________________________

_______________________

15. x 0.74

________________________

18. x 14.08

________________________

19. The average mail carrier walks 4.8 kilometers in a workday. How far do most mail carriers walk in a 6-day week? There are 27 working days in July, so how far will a mail carrier walk in July?

________________________________________ ________________________________________

20. A deli charges $3.45 for a pound of turkey. If Tim wants to purchase 2.4 pounds, how much will it cost?

________________________________________ ________________________________________

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Module 2

25 17

Practice and Problem Solving Holt McDougal Mathematics

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