<PRE><B>Question 654006</B>
An airplane, flying at top cruising speed, travels 1,680 miles in 6 hours with the wind. Against the wind, the airplane takes 7 hours at top cruising speed to travel this same distance. The wind speed is constant. What is the top cruising speed of the airplane?
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let x=top cruising speed of airplane
let c=wind speed
x+c=speed of plane with the wind
x-c=speed of plane against the wind
distance/speed=travel time
..
1680/(x+c)=6
1680/(x-c)=7
..
6x+6c=1680
7x-7c=1680
..
42x+42c=7*1680
42x-42c=6*1680
add
84x=1680(7+6)
84x=1680*13=21840
x=21840/84=260 mph
top cruising speed of airplane=260 mph

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