An airplane flies to San Francisco from Los Angeles in 4 hours. It flies back in 3 hours. If the wind is blowing from the north at a velocity of 20 mph during both flights, what was the airspeed of the plane (its speed in still air) ?

Question

Mathematics

Koen Mahoney

11 December, 19:17

An airplane flies to San Francisco from Los Angeles in 4 hours. It flies back in 3 hours. If the wind is blowing from the north at a velocity of 20 mph during both flights, what was the airspeed of the plane (its speed in still air) ?

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Answers (1)

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Olive Avila · Answer 1

Airspeed in still air: 140 mph

Step-by-step explanation:

Let s represent the speed in still air. Recognize that the distance traveled is the same in either direction.

Also note that SF is north of LA.

Distance to SF from LA = Distance to LA from SF

(s-20) (mph) (4 hr) = (s+20) (mph) (3 hr)

Then:

4s - 80 = 3s + 60 = > s = 60 + 80 + 140 (mph)

The airspeed of the plane was 140 mph in still air. With a tail wind, the plane is faster; with a headwind, slower.