Multiplying Decimals

Show your work for each problem.

1.
What is ?
1. a)0.1
2. b)1.0
3. c)100
4. d)10
Answer: 10
. Since 2.5 has 1 decimal place, move the decimal 1 place from the right: .
2.
Calculate
Answer: 9
. With 1 decimal place total, the answer is .
3.
How many decimal places will the product of have?
1. a)1
2. b)2
3. c)4
4. d)3
Answer: 2
has 1 decimal place and has 1 decimal place. Total: decimal places.
4.
Calculate
Answer: 12.6
1. Multiply as whole numbers: 126
2. How many decimal places are in the factors combined? 1
3. Place the decimal 1 place from the right in 126 12.6
5.
Calculate
Answer: 0.48
. Each factor has 1 decimal place, so the product has decimal places: .
6.
What is ?
1. a)0.345
2. b)34.5
3. c)345
4. d)3.45
Answer: 3.45
. With decimal places, the answer is .
7.
Calculate
Answer: 1.3
1. Multiply as whole numbers: 1300
2. Count total decimal places: 3.25 has ___ and 0.4 has ___. Total? 3
3. Place the decimal 3 places from the right in 1300 1.3
8.
A book costs 12.50 dollars. What is the cost of 3 books?
Answer: 37.5
1. Write the multiplication: . Multiply as whole numbers: 3750
2. How many decimal places does 12.50 have? 2
3. Place the decimal 2 places from the right in 3750 37.5
9.
Calculate
Answer: 0.1
. With decimal places: .
10.
What is ?
1. a)0.06
2. b)0.006
3. c)0.6
4. d)0.0006
Answer: 0.006
. With 4 decimal places (2 + 2), we need to add a leading zero: .
11.
Calculate
Answer: 4.2
1. Multiply as whole numbers: 4200
2. Total decimal places: 1.75 has ___ and 2.4 has ___. Total? 3
3. Place the decimal 3 places from the right in 4200 4.2
12.
Calculate
Answer: 0.02
. With 4 decimal places (2 + 2): .
13.
A rectangle has length 4.5 m and width 2.8 m. What is its area?
Answer: 12.6
1. Area = length × width. Multiply as whole numbers: 1260
2. Total decimal places in 4.5 and 2.8? 2
3. Place the decimal 2 places from the right in 1260 12.6
14.
If gas costs 1.85 dollars per liter, how much does 15.5 liters cost?
Answer: 28.675
1. Multiply as whole numbers: 28675
2. Total decimal places in 1.85 and 15.5? 3
3. Place the decimal 3 places from the right in 28675 28.675
15.
Estimate by rounding, then select the exact answer.
1. a)0.1519
2. b)15.19
3. c)151.9
4. d)1.519
Answer: 15.19
Estimation: . Exact: , with 2 decimal places = . This is close to our estimate of 15.