Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

Extension of NS2.3 Solve addition, subtraction, multiplication, and division problems, including those arising in concrete situations, that use positive and negative integers and combinations of these operations.

California Standards

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

One of the coolest summers on record in the Midwest was in 1992. The average summertime temperature that year was 66.8°F. Normally, the average temperature is 4°F higher than it was in 1992.

To find the normal average summertime temperature in the Midwest, you can add 66.8°F and 4°F.

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

Use zero as a placeholder so thatboth numbers have the same numberof digits after their decimal points.

Add each column just as you wouldadd integers.

Line up the decimal points.

70.8

66.8+ 4.0

The normal average summertime temperature in the Midwest is 70.8°F.

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

Add. Estimate to check whether the answer is reasonable.

4.55 + 11.3

Line up the decimal points.Use zero as a placeholder.

4.55+ 11.30

15.85 Add.

Estimate5 + 11 = 16 15.85 is a reasonable answer.

Example 1A: Adding and Subtracting Decimals

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

28 – 15.911

28.000 Use zeros as placeholders. –15.911

12.089 Subtract.

7 9 9 10

Line up the decimal points.

Example 1B: Adding and Subtracting Decimals

Subtract. Estimate to check whether the answer is reasonable.

Estimate28 – 16 = 12 12.089 is a reasonable answer.

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

To multiply decimals, multiply as you would with integers, and then place the decimal point. The product should have the same number of decimal places as the sum of the decimal places in the factors.

7 856 56

0.7 0.8

1 decimal place

1 decimal place

2 decimal places

+

Same digits

0.

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

Multiply. Estimate to check whether the answer is reasonable.

Example 2A: Multiplying Decimals

2.4 2

1 decimal place0 decimal places

2.4 2

4.8 1 + 0 = 1 decimal place

Estimate

2 2 = 4 4.8 is a reasonable answer.

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

Multiply. Estimate to check whether the answer is reasonable.

Example 2B: Multiplying Decimals

–3.84 0.9

2 decimal places1 decimal place

–3.84 0.9

–3.456 2 + 1 = 3 decimal places

Estimate–4 1 = –4 –3.456 is a reasonable answer.

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

To find your weight on another planet, multiply the relative gravitational pull of the planet and your weight. The relative gravitational pull on Mars is 0.38. What would a person who weighs 85 pounds on Earth weigh on Mars?

Example 3: Application

2 decimal places

0 decimal places

0.38 85

1 90

2 + 0 = 2 decimal places32.30+ 30 40

The person would weigh 32.3 pounds on Mars.

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

Add. Estimate to check whether the answer is is reasonable.

6.78 + 13.2

Line up the decimal points.Use zero as a placeholder.

6.78+ 13.20

19.98 Add.

Estimate7 + 13 = 20 19.98 is a reasonable answer.

Check It Out! Example 1A

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

Multiply. Estimate to check whether the answer is reasonable.

Check It Out! Example 2A

3.2 1.6

1 decimal place1 decimal place

3.2 1.6

1 92

1 + 1 = 2 decimal places+ 3 20

5.12

Estimate3 2 = 6 5.12 is a reasonable answer.

Holt CA Course 1

4-7 Adding, Subtracting, and Multiplying Decimals

Check It Out! Example 3

Jet fuel weighs approximately 6.2 pounds per gallon. If a plane was serviced with 1,012 gallons of fuel, how many pounds of fuel were used?

1 decimal place202 4

1 + 0 = 1 decimal place6274.4+ 6072 0

6.21,012 0 decimal places

A plane would use 6,274.4 pounds of fuel.