The formula S = D/T can be used to find the average speed of a trip, were D equals total distance traveled and T equals total time spent on the trip. Elizabeth drove half the distance of a trip at 36 mph. At what speed should she cover the remaining half in order to average 45 mph for the entire trip?

Question

The formula S = D/T can be used to find the average speed of a trip, were D equals total distance traveled and T equals total time spent on the trip. Elizabeth drove half the distance of a trip at 36 mph.  At what speed should she cover the remaining half in order to average 45 mph for the entire trip?

anonymous · Answer

The avarage can be calculated with: Avarage = (1st half + 2nd half) / 2

Since there is only 1 unknown variable it can be calculated with:

2nd half = (Avarage * 2) - 1st half

Which is: (45 * 2) - 36 = 54 mph