finding the speed of a plane

Question

A plane flies 465 miles with the wind and 345 miles against the wind in the same length of time. If the speed of the wind is 20 mph, find the speed of the plane in still air

Answer 1

d = rt, so t = d/r

 

Since the times are the same...

 

465/(r + 20) = 345/(r - 20)

465(r - 20) = 345(r + 20)

465r - 9300 = 345r + 6900

120r = 16200

r = 135

 

135 mph