Question

A man flies between two cities; on a windless day, he averages 120 mph round trip; on a windy day he averaged 140 mph with the wind; he averaged 100 mph against the wind; on the windy day, it took 15 extra minutes to make the round trip; what is the distance between the two cities?

Answer 1

let the distance be d miles
time against the wind = d/100
time with the wind = d/140

d/100 - d/140 = 1/4
times 700
7d - 5d = 175
d = 87.5

the two cities are 87.5 miles apart

check
time at slower speed = 87.5/100 = .875 hrs
times at faster speed = 87.5/140 = .625 hrs
difference = .875 - .625 = .25 hrs or 15 minutes