SOLUTION: A plane can travel 470mph with the wind and 390mph against the wind. What is the speed of the plane if the air is still?

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Question 974123: A plane can travel 470mph with the wind and 390mph against the wind. What is the speed of the plane if the air is still?
Found 3 solutions by josgarithmetic, lwsshak3, Alan3354:
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
Information is missing. What distances? Different or equal? What time quantities?

Give the complete exercise and someone could help.

Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
A plane can travel 470mph with the wind and 390mph against the wind. What is the speed of the plane if the air is still?
***
let x=speed of plane in still air
let c=speed of wind
x+c=speed of plane downwind
x-c=speed of plane against the wind
..
x+c=470
x-c=390
add
2x=860
x=430
What is the speed of the plane if the air is still? 430 mph

Answer by Alan3354(69443) About Me  (Show Source):
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It's the average of the 2 groundspeeds, and it's called airspeed.