Posted by Ed on Thursday, February 16, 2012 at 7:51am.
2 airplanes start at the same time from airports 500 km apart. Each flies with an airspeed of 200 km/hr toward the other airport. One reaches its airport half an hour before the other plane reaches the other airport. How fast is the wind blowing?

math  Reiny, Thursday, February 16, 2012 at 9:01am
let the windspeed be x km/h
time going with the wind = 500/(200+x)
time going against the wind = 500(200x)
the difference in those times = 1/2 hr
500/(200x)  500/(200+x) = 1/2
times 2(200x)(200+x)
1000(200+x)  1000(200x) = (200x)(200+x)
200000 + 1000x  2000000 +1000x = 40000  x^2
x^2 + 2000x  40000 = 0
using the quadratic formula, I got
x = 19.8 or an unreasonable 2nd answer
the windspeed is 19.8 km/h
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