Question

A plane traveled 400 miles to Rome and back. The trip there was with the wind. It took 5 hours. The trip back was into the wind. The trip back took 10 hours.
- Find the speed of the plane in still air and the speed of the wind.
Reiny
Assuming that each way is 400 miles, (even though in Rome they wouldn't know what miles are, and would be using km.)

let speed of plane in still air be x mph
let speed of wind be y mph

going with the wind:
5(x+y) = 400 ---> x + y = 80
going against the wind:
10(x-y) = 400 ---> x - y = 40

add them:
2x = 120
x = 60
then y = 20

the speed of the plane is 60 mph, and the wind has a speed of 20 mph.
(that's a pretty slow plane)
Willy
how did you get y=20