Transcript 1 decimal place - Jefferson School District

4-7
Adding, Subtracting, and Multiplying Decimals
California
Standards
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.
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
66.8
+ 4.0
70.8
Use zero as a placeholder so that
both numbers have the same number
of digits after their decimal points.
Add each column just as you would
add integers.
Line up the decimal points.
The normal average summertime temperature in
the Midwest is 70.8°F.
Holt CA Course 1
4-7
Adding, Subtracting, and Multiplying Decimals
Example 1A: Adding and Subtracting Decimals
Add. Estimate to check whether the answer is
reasonable.
4.55 + 11.3
4.55
+ 11.30
15.85
Estimate
5 + 11 = 16
Holt CA Course 1
Line up the decimal points.
Use zero as a placeholder.
Add.
15.85 is a reasonable answer.
4-7
Adding, Subtracting, and Multiplying Decimals
Example 1B: Adding and Subtracting Decimals
Subtract. Estimate to check whether the
answer is reasonable.
28 – 15.911
7 9 9 10
28.000
–15.911
12.089
Estimate
28 – 16 = 12
Holt CA Course 1
Use zeros as placeholders.
Line up the decimal points.
Subtract.
12.089 is a reasonable answer.
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
8
56
0.7
 0.8
0.56
Same digits
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1 decimal place
+ 1 decimal place
2 decimal places
4-7
Adding, Subtracting, and Multiplying Decimals
Example 2A: Multiplying Decimals
Multiply. Estimate to check whether the answer
is reasonable.
2.4  2
2.4
 2
4.8
1 decimal place
0 decimal places
1 + 0 = 1 decimal place
Estimate
22=4
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4.8 is a reasonable answer.
4-7
Adding, Subtracting, and Multiplying Decimals
Example 2B: Multiplying Decimals
Multiply. Estimate to check whether the answer
is reasonable.
–3.84  0.9
–3.84
 0.9
–3.456
Estimate
–4  1 = –4
Holt CA Course 1
2 decimal places
1 decimal place
2 + 1 = 3 decimal places
–3.456 is a reasonable answer.
4-7
Adding, Subtracting, and Multiplying Decimals
Example 3: Application
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?
0.38
 85
1 90
+ 30 40
32.30
2 decimal places
0 decimal places
2 + 0 = 2 decimal places
The person would weigh 32.3 pounds on Mars.
Holt CA Course 1
4-7
Adding, Subtracting, and Multiplying Decimals
Check It Out! Example 1A
Add. Estimate to check whether the answer is
is reasonable.
6.78 + 13.2
6.78
+ 13.20
19.98
Line up the decimal points.
Use zero as a placeholder.
Add.
Estimate
7 + 13 = 20 19.98 is a reasonable answer.
Holt CA Course 1
4-7
Adding, Subtracting, and Multiplying Decimals
Check It Out! Example 2A
Multiply. Estimate to check whether the
answer is reasonable.
3.2  1.6
3.2
 1.6
1 92
+ 3 20
5.12
Estimate
32=6
Holt CA Course 1
1 decimal place
1 decimal place
1 + 1 = 2 decimal places
5.12 is a reasonable answer.
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?
1,012
 6.2
202 4
+ 6072 0
6274.4
0 decimal places
1 decimal place
1 + 0 = 1 decimal place
A plane would use 6,274.4 pounds of fuel.
Holt CA Course 1