A commuter plane flies to a small town from a major airport

A commuter plane flies to a small town from a major airport. The average speed flying to the small town was 240mph and the average speed returning was 180mph. The total flying time was 7hr. Find the distance between the two airports..

Solution

Let the distance between major airport , d :

average speed flying to the small town was 240mph

Time t1 = d/240

average speed returning was 180mph

Time t2 = d/180

d/240 + d/180 = 7

(d/30){ 1/8 +1/6) =7

(d/30) { 14/48} = 7

d = 7*48*30/14 = 720 miles