7th Grade Math

408 Linear Functions

Example 1 1. BAKING The number of cakes baked varies Cake Baking

Cakes

20

40

0

60

80

Hours

2468

directly with the number of hours the caterers

work. What is the ratio of cakes baked to

hours worked?

Example 2 2. TRANSPORTATION An airplane travels 780 miles

in 4 hours. Make a table and graph to show

the mileage for 2, 8, and 12 hours. Is there a

direct variation?

Examples 3 and 4 3. Determine whether the linear function is a direct

variation. If so, state the constant of variation.

Hours, x 3579

Miles, y 108 180 252 324

= Step-by-Step Solutions begin on page R1.

Extra Practice begins on page EP2.

4. GARDENING Veronica is mulching
   her front yard. The total weight of
   mulch varies directly with the
   number of bags of mulch. What is
   the rate of change?
   Mulch
   y

Weight (lb)

Bags

60

90

150

30

120

0

180

210

12 34 5 67

55 DOG WALKING The money Shelley

earns varies directly with the

number of dogs she walks. How

much does Shelley earn for each

dog she walks?

Dog Walking

y

Pay ($) 6

4

2

8

10

12

14

Dogs

0 12 34 5 67

Determine whether each linear function is a direct variation. If so, state the

constant of variation.

Examples 2–4

6. Pictures, x 3456
   Profit, y 24 32 40 48
   7. Minutes, x 185 235 275 325
   Cost, y 60 115 140 180


7. Age, x 11 13 15 19
   Grade, y 57911


8. Price, x 20 25 30 35
   Tax, y 4567

B 10. PRESSURE At a 33-foot depth underwater, the pressure is 29.55 pounds

per square inch (psi). At a depth of 66 feet, the pressure reaches 44.4 psi.

At what rate is the pressure increasing?

Example 1

404_415_C07_L3_895130.indd 408 12/31/09 4:33 PM