An airplane takes 5 hours to travel a distance of 3400km against the wind. The return trip takes 4 hours with the wind. What is the rate of the plane in still air and what is the rate of the wind?

Against the wind:

distance = 3400 km

time = 5 hr.

rate = d/t = 3400/5 = 680 km/hr

With the wind:

distance = 3400 km

time = 4 hr

rate = d/t = 3400/4 = 850 km/hr

Equations:

plane speed - wind speed = 680 km/hr

plane speed + wind speed = 850 km/hr

2 (plane speed) = 1530

plane speed = 765 km/hr

Substitute and solve for "wind speed":

765 + wind speed = 850

wind speed = 85 km/hr

Did you follow?