# Math Is Fun Forum

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## #1 2006-12-21 10:24:07

unique
Member
Registered: 2006-10-04
Posts: 419

### speed in still air

A fighter plane could fly at 4 times the speed of the wind. as a result, it could travel 60 miles downwind in 1 hour longer than it took to travel 300 miles upwind. what waas the fighter plane's speed in  still air?

Desi
Raat Key Rani !

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## #2 2006-12-21 10:57:12

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,588

### Re: speed in still air

I think you have upwind and downwind mixed up, or else I have their definitions messed up.
Downwind is with the wind I thought, and upwind is against the wind.

igloo myrtilles fourmis

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## #3 2006-12-21 11:25:35

unique
Member
Registered: 2006-10-04
Posts: 419

### Re: speed in still air

OH MY GOD i messed it up.....
A fighter plane could fly at 4 times the speed of the wind. as a result, it could travel 600 miles downwind in 1 hour longer than it took to travel 300 miles upwind. what waas the fighter plane's speed in  still air?

But the upwind and downwind thing is right.

Desi
Raat Key Rani !

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## #4 2006-12-21 12:07:09

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,588

### Re: speed in still air

Let's see, uh, 5 times wind speed times (uptime + 1) = 2 (3 times wind speed times uptime).
600 = 5w(u+1) = 6wu
600 = 5wu + 5w = 6wu
Make into 2 equations and subtract 5/6ths of equation from the other and
solve for w, the wind speed.
100 = 5w
wind speed = 20mph
plane speed = 80 in still air.
Didn't check answer.  You can.  (as Krassi would say)

igloo myrtilles fourmis

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