Question

The time, t, required to drive to a certain distance varies inversely with the speed, r. if it takes 12 hours to drive the distance at 60 miles per hour, how long will it take to drive the same distance at 85 miles per hour ?
A. about 7.08 hours
B. about 5.00 hours
C. about 1.42 hours
D. about 8.47 hours

Answer 1

T = k/R  where k is the constant of variation, T=time and R=speed.
Plug in the given values:-
12 = k/60
k = 12*60 = 720
So the equation of variation is T = 720/R

At 85 mph we have

T = 720 / 85 =  8.47 hours (answer)