Thirty years ago, police would check a highway for speeders by sending a helicopter up in the air and observing the time it would take for a car to travel between two wide lines placed 1/10th of a mile apart. On one occasion, a car was observed to take 7.2 seconds to travel this distance. What is the speed of this car in miles per hour?

Work Shown:

1/10 = 0.1

0.1 mile = 7.2 seconds

1 mile = 72 seconds (multiply both sides by 10)

1/72 mile = 1 second (divide both sides by 72)

3600/72 = 3600 seconds (multiply both sides by 3600)

50 miles = 3600 seconds

50 miles = 1 hour

The car's speed is 50 mph

Note: 1 hour = 60 min = 60*60 = 3600 seconds

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional