# Precalculus 11

posted by Kayla

Hello,

An airplane makes a 990 km flight with a tailwind & returns, flying into the same wind. The total flying time is 3 hrs 20 mins & the airplanes speed in still air is 600 km/hr what is the the speed of the wind?

I'm as far as (990/(600-x))+(990/600+x))=10/3

but I can't figure out how to go from there!

Thanks a bunch :)
Kayla

1. bobpursley

same distance, there and back
v1*t1=v2*t2=990km
t1=3 1/3 hr -t2

v1=600+w
v2=600-w

(600+w)t1=990 or
t1=990/(600+w)
10/3-t1=990/(600-w)

10/3-990/(600+w) = 990/(600-w) so your equation is correct.

now, multipy each side by (600-w)(600+w)/990

10(600^2-w^2)/(3*990) = 600+w+600-w)
check that. Now is simplifies considerably, gather terms, and you have a quadratic equation. use the quadratic formula.

2. scott

multiply by the LCD

[990 (600 + x)] + [990 (600 - x)] = 10/3 (600 - x)(600 + x)

1188000 = 10/3 (360000 - x^2) ... 356400 = 360000 - x^2

x^2 = 3600

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