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PS:average speed

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Senior Manager
Senior Manager
User avatar
Joined: 16 Jan 2009
Posts: 362
Concentration: Technology, Marketing
GMAT 1: 700 Q50 V34
GPA: 3
WE: Sales (Telecommunications)
Followers: 2

Kudos [?]: 67 [0], given: 16

GMAT Tests User
PS:average speed [#permalink] New post 30 Jun 2009, 23:07
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

50% (00:00) correct 50% (00:00) wrong based on 3 sessions
A bus trip of 450 miles would have taken 1 hour less if the average speed S for the trip had been greater by 5 miles per hour. What was the average speed S, in miles per hour, for the trip?
(A) 10
(B) 40
(C) 45
(D) 50
(E) 55
_________________

Lahoosaher

Senior Manager
Senior Manager
avatar
Joined: 23 Jun 2009
Posts: 360
Location: Turkey
Schools: UPenn, UMich, HKS, UCB, Chicago
Followers: 5

Kudos [?]: 95 [0], given: 60

GMAT Tests User
Re: PS:average speed [#permalink] New post 30 Jun 2009, 23:36
Time=distance/avg.speed.
Time1=450/S,
Time2=Time1-1=450/(S+5)
Gathering both together
450/(S+5)=450/S-1
450/(S+5)=(450-S)/S
450*S=(450-S)*(S+5)
450S=450S+2250-S^2-5S
S^2+5S-2250=0
Solving the root
(-5+95)/2= 45
S=45
Time1=10
s+5=50
Time2=9
;)
Senior Manager
Senior Manager
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Joined: 25 Mar 2009
Posts: 305
Followers: 6

Kudos [?]: 66 [0], given: 6

GMAT Tests User
Re: PS:average speed [#permalink] New post 02 Jul 2009, 10:45
R*T = D

Slower trip (1 hour more):
S * (T + 1) = 450

Faster trip (1 hour less):
(S + 5) * T = 450

S*(T+1) = (S+5)*T
ST + S = ST + 5T
S = 5T

Plug in this value of S into the first equation:
5T*(T+1) = 450
T*(T+1) = 90
T = 9

S = 5T = 5*9 = 45

C
Re: PS:average speed   [#permalink] 02 Jul 2009, 10:45
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