SOLUTION: The speed of a plane is 120 miles per hour in a calm. With the wind it can cover a certain distance in 4 hours, but against the wind it can cover only 3/5 of that distance in the s

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Question 150819: The speed of a plane is 120 miles per hour in a calm. With the wind it can cover a certain distance in 4 hours, but against the wind it can cover only 3/5 of that distance in the same time. Find the velocity of the wind.
Answer by nerdybill(7384) (Show Source):
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The speed of a plane is 120 miles per hour in a calm. With the wind it can cover a certain distance in 4 hours, but against the wind it can cover only 3/5 of that distance in the same time. Find the velocity of the wind.
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Let x=velocity of the wind
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distance with wind = 4(120+x)
distance against the wind = 4(120-x)
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(3/5)(4)(120+x) = 4(120-x)
(3/5)(120+x) = (120-x)
(3)(120+x) = 5(120-x)
360+3x = 600-5x
360+8x = 600
8x = 240
x = 30 mph