Answer:
440 mph would be the speed of the plane in still air.
Explanation:
Note that with wind, a plane can travel 480. Against wind, it is 400. This means that if there is no wind, technically the amount would be in the middle of the two numbers given. Find the mean:
(480 + 400)/2 = Answer
Answer = (880)/2
Answer = 440
440 mph would be the speed of the plane in still air.
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