Problema Solution
A plane can fly 120 mph in calm air. Flying with the wind, the plane can fly 399 mi in the same amount of time it takes to fly 321 mi against the wind. Find the rate of the wind.
Answer provided by our tutors
let
v = 120 mph the speed of the plane in calm air
w = the rate of the wind
v + w = the speed of the plane flying with the wind
v - w = the speed of the plae flying against the wind
since speed = distance / time follows time = distance/speed:
399/(v + w) = 321/(v - w)
399/(120 + w) = 321/(120 - w)
by solving we find:
w = 13 mph
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the rate of the wind is 13 mph.