Worked-out Problems

Chapter 3 continued
18. 2
x 4 12
2
x 4 4 12 4
2
x 8
2 2
x 2(8)
x 16
Check: 2
x 4 12
( 16)
4
2
12
12 12 ✓
19. 5 19 7
x
5 19 19 7
x 19
14 7
x
7(14) 7 7
x
98 x
Check: 5 19 7
x
5 19 ( 98)
7
5 5 ✓
20. a. Given: You begin with 16 gallons of gasoline. You
use 3 gallons of gasoline per hour of driving. You will
stop when there is 1 gallon of gasoline left.
Find: When will you stop to refuel?
b. Sample answer: Let h the number of hours.
Total
gallons
Gallons Number
p
per hour of hours
16 3h 1
c. 16 1 3h 1 1
15 3h
1 5
3 h
3 3
Gallons
left
5 h
You will need to stop and refuel after 5 hours.
Hours of Gallons of
driving gasoline left
0 16
1 13
2 10
3 7
4 4
5 1
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All rights reserved.
21. Let x the discount per person.
Price with Price without Number
p
discount discount of people
729 810 9x
729 810 810 9x 810
81 9x
81
9
9x
9
9 x
The discount per person is $9.
22. Let x the weight of one car.
Total Weight of Number
p
weight locomotive of cars
4725 125 50x
4725 125 125 50x 125
4600 50x
46 00
5 0x
50
50
92 x
Each car weighs 92 tons.
23. 5 2x 7
5 2x 5 7 5
2x 2
2x
2
2
2
x 1
24. 32 9x 140
32 9x 32 140 32
9x 108
9
x
9
1 08
9
x 12
25. 13 6x 67
13 6x 13 67 13
6x 54
6 x
5 4
6 6
x 9
26. 8 3x 19
8 3x 8 19 8
3x 27
3x
27
3
3
x 9
Chapter 3
Discount
per person
Weight of
one car
Pre-Algebra 71
Worked-Out Solution Key