7th Grade Math

Selected Answers and Solutions R21

Selected Answers and Solutions

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3 x = 78 Simplify.

_^33 x = _^783 Divide each side by 3.

x = 26 yards Simplify.

An object that is 78 feet long is 26 yards long.

19a. 10 gal per minute; yes

19b.

40

30

50

20

10

0

60

70

80

90

100

110

15782 3 46

Time (min)

Number of Gallons

19c. Sample answer: g = 10 m 21. Sample answer:

x = 9, y = 5 _ 21 ; x = 36; y = 22 25. G 27. a speed of

45 mph; the distance driven on Day 1

29. no; Sample answer: Possible times and
    distances are shown in the table. Since _distancetime
    ratios are not equal, the relationship is not
    proportional.
    Time (h) 1234
    Distance (mi) 145 190 235 280

Pages 414–415 Lesson 7-3E

11 Determine if the relationship is an inverse

variation by checking that xy = k for some

constant k.

48(360) = 17,280; 36(480) = 17,280; 24(720) = 17,280;

12(1,440) = 17,280

The relationship is an inverse variation.

Frequency (cycles/s)

640

320

0

960

480

160

800

1,120

1,280

1,440

1,600

10 20 30 40 50 60 70 8090

Length (in)

Piano Strings

3.

Width (m)

8

4

0

12

6

2

10

14

16

18

246810121416

Length (m)

yes

5. 24 h
   77 Check if it is a direct variation by looking at
   the ratio of each pair of numbers.
   882 or 44, ^444 or 11. The relationship is not a direct
   variation.
   Next, check to see if the relationship is an inverse
   variation.
   88(2) = 176, 44(4) = 176; The relationship is an
   inverse variation.


6. Sample answer: x = 12, y = 2; x = 6, y = 4;
   x = 8, y = 3. 11. B 13. A 15. Sample answer:
   200 stamps
   Pages 418–421 Chapter Study Guide and Review


7. slope 3. inverse variation 5. function


8. function table 9. constant rate of change


9. rate of change


10. x 2 xy

12 × 12

22 × 24

32 × 36

42 × 48

Domain: {1, 2, 3, 4};

Range: {2, 4, 6, 8}

15.

Total Words

60

031 24

40

80

20

100

Time (min)

Texting Rate

y

x

17. y

0 x

2

4

6

8

10

12

14

1234

19. 2 laps per minute 21. 3 ft per yd


20. 
    

Inches

3

2

4

1

0

5

Time (hr)

152 3 4

Rainfall Slope =^ _^21 or 2; for every

1 hour of rainfall,

2 inches of rain will

accumulate

R01_R42_EM_SelAns_895130.indd R21 1/18/10 9:51 AM