What was the air force plane's average speed in the outbound trip?

Question

An air force plane flew to Dublin and back. the trip there took 12 hours. It averaged 85 mph faster on the trip there than on the return trip. What was the air force plane's average speed in the outbound trip?

Answer 1

If s miles is the distance to Dublin, then s=12v where v mph is the outbound average speed.

s=(v-85)t where t is the time for the return journey.

So 12v=(v-85)t, 12v=vt-85t, v=85t/(t-12).

There is insufficient information (for example, the return time) to quantify the outbound speed, v.

EXAMPLE

If t=13hrs, v=1105mph. If t=14hrs, v=595mph. If t=13.5hrs, v=765mph.