7th Grade Math

R20 Selected Answers and Solutions

Selected Answers and Solutions

So, the constant rate of change is about 0.02 mile

per second.

b.

Distance (miles)

3

2

4

1

0

5

Time (seconds)

(^50100150200250300)
Go-Kart Racing Times

11. Sample answer: At Sam’s Shoes, 2 pairs of
    sandals cost $30 and 4 pairs cost $60. Find the rate
    of change. 13. 390 15. nonlinear; the rate of
    change is not constant

Pages 398–399 Lesson 7-2C

11

0

32

28

24

20

16

12

12345678

8

4

Number of Boxes

Number of Packs

The slope of the line is equal to the rate at which

the number of fruit snacks increases as the number

of boxes increases or __8 fruit snacks1 box. 8 packs per box;

The slope represents how many packages of fruit

snacks are in each box.

3. y

0 x

8

9

10

7 6 5 4 3 2

9182736455463728190

1

Distance (km)

Time (min)

9 _ 1 or 9; Adriano

traveled 9

kilometers per

minute.

5.

2

4

6

8

1 2 3 4

1

3

5

7

9

0

Number of Yards

Number of Feet

_^3

1 or 3; There are 3 feet

per yard.

77 a. The point (2, 120) represents the fact that

Car A had traveled 120 miles in 2 hours. b. The

point (1.5, 67.5) represents the fact that Car B had

traveled 67.5 miles in 1.5 hours. c. The ratio

of the change in y-coordinate to the change in

x-coordinate for each pair of points represents the

average speed of each vehicle. d. The slope of

each line represents the average speed of each

vehicle. e. Car A is traveling faster. Since its graph

is rising more rapidly, its speed is greater.

9. Marisol found runrise. Her answer should be ^32.


10. _^41 or 4 13. $9 per hour

Pages 402–403 Lesson 7-3A

1. Sample answer: Graphs provide a visual
   representation of a situation involving
   comparisons. A graphical model can sometimes
   show conclusively what is often diffi cult to
   interpret from looking at lists alone.
   3a.

Temperature in Fahrenheit

40

20

0

120

60

80

100

5 1015202530354045

Temperature in Celsius

Temperature Conversions

3b. Sample answer: 77°F 5. 158, 318 7. Wednesday

99 If the helicopter can carry 2,400 pounds and

the crates weigh 75 pounds each, divide 2,400 by 75

to fi nd the amount of crates the helicopter can

carry; 2,400 ÷ 75 = 32 crates

11. 18

Pages 408–410 Lesson 7-3C

1. 30 cakes per hour 3. yes; 36
   55 Since the points on the graph lie in a straight
   line, the rate of change is a constant. The constant
   ratio is what Shelley makes per dog.
   pay ($) →
   number of dogs →^

_^10

4 or $2.50,

_^5

2 or $2.50

Shelley makes $2.50 per dog.

7. no 9. yes; 0.2 11. $0.80/book 13. y =^15 _ x; 3


8. y = ^78 x; 16
   1717 Since we are given that a direct variation exists,
   we can fi nd the constant of variation from one
   point on the graph. Using the point (36, 12) we fi nd
   that the constant of variation is ^3612 or ^31. Use this
   fact to set up and solve a proportion to fi nd the
   measure of an object in yards if it is 78 feet long.
   13 =^78 _x Set up the proportion.
   3 · x = 1 · 78 Find the cross products.

R01_R42_EM_SelAns_895130.indd R20 1/18/10 9:51 AM