Linear inequality word problems

Question

A car traveling 60 miles per hour approaches an area with a 50 mph speed limit. In order to reduce the speed to 50 mph or less, the driver slows down the car at a constant rate of 15 feet per second squared (ft/s²) for t seconds. Which of the following inequalities best describes the situation?

1 mile = 5,280 and 1 hour = 3,600 seconds

Answer Choices:

A.60−15t > 50

B.88−15t ≤ 73.3

C.88+15t ≤ 73.3

D.88+15t > 73.3

Answer 1

50 mph = 50*5280/3600= 73.3 f/s and 60 mph = 60*5280/3600= 88 f/s. The speed of the car = S= S_initialth + at =88 f/s and a = -15f/s thus S=88-15t. So if S<=73.3 then 73.3>=88-15t. Re-arrange to get 88-15t<=73.3 or B.