Section 5'4 Multiplying Signed Decimal Numbers

1
Section 5.4 Multiplying Signed Decimal Numbers
Steps for Multiplying Decimals 1. Ignore
decimals and multiply as before 2. Count the
number of digits after the decimal in the
original problem and make sure the answer has
the same number of digits after the decimal.
2
Simplify the following
1. 0.07(0.03) 2. 0.42(6)
7 ( 3 )
- 42 ( 6 )
21
- 252
2 decimal places
4 decimal places
-2.52
0.0021
3
3. 3.12(0.05) 4. 0.02(1.39)
312 ( 5 )
- 2 ( -139 )
1560
278
4 decimal places
4 decimal places
0.0278
0.1560
4
5. 1.22 6. (- 0.3)2
1.2 ( 1.2 )
- 0.3 ( - 0.3 )
12 ( 12 )
- 3 ( - 3 )
144
9
0.09
1.44
5
7. 0.5(22) 8. 10(.314)
5 ( 22 )
10 ( 314 )
3140
110
11.0
3.14
6
9. 100(.314) 10. 1000(.314)
100 ( 314 )
1000 ( 314 )
314000
31400
31.4
314
7
11. What is the perimeter of a rectangular
field that measures 4.2 miles by 3.1 miles?
P 2l 2w
P 2(4.2) 2(3.1)
P 2(42) 2(31)
P 84 62
8.4 6.2
P 8.4 6.2
The perimeter of the rectangular field is 14.6
miles.
8
12. What is the area of a rectangular field
that measures 4.2 miles by 3.1 miles?
A bh
A (4.2)(3.1)
A (42)(31)
A 1302
A 13.02
The area of the rectangular field is 13.02 square
miles.
9
13. John worked 63.5 hours over the past two
weeks. John earns 9.50 per hour. How much money
did John earn?
Johns earnings (63.5)(9.50)
Johns earnings (635)(95)
Johns earnings 60325
Johns earnings 603.25
John earned 603.25.
10
14. Jill filled up the gas tank in her new
hybrid car. Jill put 10.39 gallons of gas in
her car at a rate of 2.39 per gallon. How much
did she pay for gas?
Gas Bill (10.39)(2.39)
Gas Bill (1039)(239)
Gas Bill 248321
Gas Bill 24.83
Jill purchased 24.83 worth of gas.
11
15. What is the volume of a rectangular cube
with dimensions 3.2 feet by 4.1 feet by 1.1
feet?
Volume (3.2)(4.1)(1.1)
V (32)(41)(11)
V 14432
V 14.432
The volume of the rectangular cube is 14.432ft3.
12
Sec 5.4 Multiplying decimals Pg. 337 9 19
odd, 39 59 odd, 10, 16, 40, 48, 54
13

• Section 5.5 Dividing Signed Decimal Numbers
• Steps for dividing by whole numbers
• Use long division as if there were no decimal
  point involved.
• If necessary, add zeros after last digit in the
  decimal.
• 3. Place decimal point directly above the
  decimal point in the problem.

14
Divide the following
4
7
6
5
8
7
0
32
-28
5
2
-3
4
48
-32
-2
8
4
0
-28
40
0
0
15
Steps for dividing by decimals numbers 1.
Change divisor to a whole number by moving both
numbers the same amount of digits 2. Divide
as before
16
6
6
6
Divide the following
198
21
7
198
19
8
198
0
17
Divide the following
3
3
66
6
6
66
0
18
5. .3778 .25 and round to the nearest
hundredth
When rounding make sure to calculate one digit
past required place value.
1
5
1.51
1
1
0
25
12
7
125
2
8
25
3
0
25
19
6. 4.579 34.8 (4)
-8
7
4.579 34.8 (4)
32
4.579 ( -8.7 )
2
8
28
0
- 8.700 4.579
-4.121
20
7. (3.07 0.43) 0.33
3.07 0.43
(3.07 0.43) 0.33
2.64
2.64 0.33
8
8
264
0
21
0.3 (0.3)
8. 6 (0.3)2 10
3 (3)
6 (0.3)2 10
9
6 0.09 10
0.09
6 0.09 10
0
0
9
6 0.009
0
6 0.009
.000
90
0
5.991
22
9. Jill filled up the gas tank in her new hybrid
car. Jill put 10.3 gallons of gas in her car and
she had driven 473.8 miles. Estimate the gas
mileage then determine how many miles per gallon
her car achieved?
47 mpg
470 miles 10 gallons
23
9. Jill filled up the gas tank in her new hybrid
car. Jill put 10.3 gallons of gas in her car and
she had driven 473.8 miles. Estimate the gas
mileage then determine how many miles per gallon
her car achieved?
47 mpg
4
6
Jill can get 46 miles per gallon while driving
her hybrid car.
412
61
8
618
0
24
Sec 5.5 Dividing decimals Pg. 349 1 6 all,
9, 10, 12, 15, 35 59 odd, 42, 60