1. 3-5 Multiplying Decimals Warm Up Problem of the Day
Course 1
Warm Up
Problem of the Day
Lesson Presentation

2. 3-5 Multiplying Decimals Warm Up Multiply. 1. 87  320 27,840
Course 1
3-5
Multiplying Decimals
Warm Up
Multiply.
1. 87  320
27,840
 800
754,400
3. 3,806  10
38,060
4. 1,207  100
120,700
5. 72  196
14,112
 523
62,760

3. 3-5 Multiplying Decimals Problem of the Day
Course 1
3-5
Multiplying Decimals
Problem of the Day
Carmen and Rita sold homemade oatmeal cookies. After 8 days, they had sales totaling $70. Each day, their sales were $0.50 higher than the previous day. What were their sales on the first day?
$7.00

4. 3-5 Multiplying Decimals
Course 1
3-5
Multiplying Decimals
Learn to multiply decimals by whole numbers and by decimals.

5. Additional Example 1: Science Application
Course 1
3-5
Multiplying Decimals
Additional Example 1: Science Application
Something that weighs 1 lb on Earth weighs 0.17 lb on the Moon. How much would a 4 lb dumbbell weigh on the Moon?
Multiply 4 by 0.17, since 1 pound on Earth is 0.17 pound on the Moon.
4  0.17 17
Multiply as you would with whole numbers.
 4 68

6. Additional Example 1 Continued
Course 1
3-5
Multiplying Decimals
Additional Example 1 Continued
Something that weighs 1 lb on Earth weighs 0.17 lb on the Moon. How much would a 4 lb dumbbell weigh on the Moon?
Place the decimal point by adding the number of decimal places in the numbers multiplied.
0.17
2 decimal places
 4
+ 0 decimal places
0.68
2 decimal places
A 4 lb dumbbell on Earth weighs 0.68 lb on the Moon.

7. 3-5 Multiplying Decimals  7 Check It Out: Example 1
Course 1
3-5
Multiplying Decimals
Check It Out: Example 1
Something that weighs 1 lb on Earth weighs 0.17 lb on the Moon. How much would a 7 lb dumbbell weigh on the Moon?
Multiply 7 by 0.17, since 1 pound on Earth is 0.17 pound on the Moon.
7  0.17 17
Multiply as you would with whole numbers.
 7
119

8. Check It Out: Example 1 Continued
Course 1
3-5
Multiplying Decimals
Check It Out: Example 1 Continued
Something that weighs 1 lb on Earth weighs 0.17 lb on the Moon. How much would a 7 lb dumbbell weigh on the Moon?
Place the decimal point by adding the number of decimal places in the numbers multiplied.
0.17
2 decimal places
 7
+ 0 decimal places
1.19
2 decimal places
A 7 lb dumbbell on Earth weighs 1.19 lb on the Moon.

9. 3-5 Multiplying Decimals Helpful Hint
Course 1
3-5
Multiplying Decimals
You can use a decimal grid to model multiplication of decimals.
Helpful Hint

10. Additional Example 2A: Multiplying a Decimal by a Decimal
Course 1
3-5
Multiplying Decimals
Additional Example 2A: Multiplying a Decimal by a Decimal
Find the product.
0.3  0.4
Multiply. Then place the decimal point.
1 decimal place
0.3 
+ 1 decimal place
0.4
2 decimal places
0.12

11. Additional Example 2B: Multiplying a Decimal by a Decimal
Course 1
3-5
Multiplying Decimals
Additional Example 2B: Multiplying a Decimal by a Decimal
0.07  0.8
Estimate the product. 0.8 is close to 1.
0.07  1 = 0.07
Multiply. Then place the decimal point.
2 decimal places
0.07
 0.8
+ 1 decimal place
3 decimal places; use a placeholder zero
0.056
0.056 is close to the estimate of The answer is reasonable.

12. Additional Example 2C: Multiplying a Decimal by a Decimal
Course 1
3-5
Multiplying Decimals
Additional Example 2C: Multiplying a Decimal by a Decimal
1.34  2.5
Estimate the product. Round each factor to the nearest whole number.
1  3 = 3
Multiply. Then place the decimal point.
1.34 
2.5
2 decimal places
670
+ 1 decimal place
2680
3 decimal places
3.350
3.350 is close to the estimate of 3. The answer is reasonable.

13. 3-5 Multiplying Decimals  Check It Out: Example 2A Find the product.
Course 1
3-5
Multiplying Decimals
Check It Out: Example 2A
Find the product.
0.5  0.2
Multiply. Then place the decimal point.
1 decimal place
0.5 
+ 1 decimal place
0.2
2 decimal places
0.10

14. 3-5 Multiplying Decimals  Check It Out: Example 2B 0.03  0.9
Course 1
3-5
Multiplying Decimals
Check It Out: Example 2B
0.03  0.9
Estimate the product. 0.9 is close to 1.
0.03  1 = 0.03
Multiply. Then place the decimal point.
0.03
2 decimal places 
0.9
+ 1 decimal place
0.027
3 decimal places; use a placeholder zero
0.027 is close to the estimate of The answer is reasonable.

15. 3-5 Multiplying Decimals  Check It Out: Example 2C 3.80  3.3
Course 1
3-5
Multiplying Decimals
Check It Out: Example 2C
3.80  3.3
Estimate the product. Round each factor to the nearest whole number.
4  3 = 12
Multiply. Then place the decimal point.
3.80 
3.3
2 decimal places
1140
+ 1 decimal places
11400
3 decimal places
12.540
12.54 is close to the estimate of 12. The answer is reasonable.

16. Additional Example 3A: Evaluating Decimal Expressions
Course 1
3-5
Multiplying Decimals
Additional Example 3A: Evaluating Decimal Expressions
Evaluate 5x for the value of x.
x = 3.062
Substitute for x.
5x = 5(3.062)
3 decimal places
3.062  5
+ 0 decimal places
15.310
3 decimal places
These notations all mean multiply 3 times x.
3 • x 3x 3(x)
Remember!

17. Additional Example 3B: Evaluating Decimal Expressions
Course 1
3-5
Multiplying Decimals
Additional Example 3B: Evaluating Decimal Expressions
Evaluate 5x for the value of x.
x = 4.79
Substitute 4.79 for x.
5x = 5(4.79)
2 decimal places
4.79  5
+ 0 decimal places
23.95
2 decimal places

18. 3-5 Multiplying Decimals  Check It Out: Example 3A
Course 1
3-5
Multiplying Decimals
Check It Out: Example 3A
Evaluate 5x for the value of x.
x = 2.012
Substitute for x.
5x = 5(2.012)
3 decimal places
2.012  5
+ 0 decimal places
10.060
3 decimal places

19. 3-5 Multiplying Decimals  Check It Out: Example 3B
Course 1
3-5
Multiplying Decimals
Check It Out: Example 3B
Evaluate 5x for the value of x.
x = 6.22
Substitute 6.22 for x.
5x = 5(6.22)
2 decimal places
6.22  5
+ 0 decimal places
31.10
2 decimal places

20. Insert Lesson Title Here
Course 1
3-5
Multiplying Decimals
Insert Lesson Title Here
Lesson Quiz
Find each product.
 0.07
Evaluate 8x for each value of x.
 0.07
0.056
3. x = x = 0.804
21.64
6.432
5. “Pick your own” peaches sell for $0.95 per pound. You picked 92 pounds of peaches. How much were you charged?
$87.40