Question

Two brothers leave from the same point driving in opposite​ directions, the first brother driving at 60 miles per hour and the second at 65 mph. The first brother has a​ one-hour head start. If each brother has a communication device that allows him to talk to the other for up to a 200​-mile ​range, how long will they be able to talk to each​ other?

The communication devices will be out of range __ hours after the first brother left.

Answer 1

2.12 hours

Explanation:

The distance between the brothers after t hours will be ...

distance = speed × time

d = 60t +65(t -1) . . . . . . for t > 1

We want to find t when the distance is 200 miles:

200 = 125t -65

265/125 = t = 2.12

The communication devices will be out of range 2.12 hours after the first brother left.