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# A plane flying against the wind covers a 900 kilometer route

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Manager
Joined: 12 Feb 2006
Posts: 115
Followers: 1

Kudos [?]: 29 [0], given: 0

A plane flying against the wind covers a 900 kilometer route [#permalink]  28 Feb 2007, 02:00
A plane flying against the wind covers a 900 kilometer route in 2 hours. The same plane flying with the wind covers the same 900 kilometer route in 1.8 hours. If the speed of the wind is constant what is the speed of the wind?

18 KMH
20 KMH
22 KMH
25 KMH
27 KMH
SVP
Joined: 01 May 2006
Posts: 1798
Followers: 8

Kudos [?]: 102 [0], given: 0

(D) for me

Let set those variables:
o V : the speed of the aircraft in KM/H when there is no wind
o v : the speed of the wind.

Then, we have those equations from the 2 trips
o 900/2 = V-v (1)
o 900/1,8 = V+v (2)

Finally,
(2)-(1) <=> 900*(1/1,8 - 1/2) = 2*v
<=> v = 900 / 2 * (10/18 - 9/18) = 900/2 * 1/18 = 100/4 = 25
VP
Joined: 09 Jan 2007
Posts: 1045
Location: New York, NY
Schools: Chicago Booth Class of 2010
Followers: 10

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Re: Help with a Rate Question [#permalink]  28 Feb 2007, 02:43
bz9 wrote:
A plane flying against the wind covers a 900 kilometer route in 2 hours. The same plane flying with the wind covers the same 900 kilometer route in 1.8 hours. If the speed of the wind is constant what is the speed of the wind?

18 KMH
20 KMH
22 KMH
25 KMH
27 KMH

Airplane Speed=A
Wind Speed=W

A-W=900/2=450 Km/h
A+W=900/1.8=500Km/h

Solving for W=25Km/h (D)
Re: Help with a Rate Question   [#permalink] 28 Feb 2007, 02:43
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