SOLUTION: A courier who travels at the rate of 6.5 mi/hour is followed, after 30 minutes, by another who travels at the rate of 7.5 mi/hour. After how many more hours will the second over

From the point of view of the second courier, the first courier has a head-start of 6.5 miles x 0.5 of an hour,

which is, actually, 3.25 miles.


Every hour, the second courier diminishes the distance between them at the rate of (7.5-6.5) = 1 miles per hour.


Hence, the second courier will overtake the first one in  = 3.25 hours = 3  hours = 3  hours = 3 hours and 15 minutes.