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# How many hours did it take Helen to drive from her house to

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Intern
Joined: 16 Jul 2008
Posts: 13
How many hours did it take Helen to drive from her house to [#permalink]

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23 Jul 2008, 22:50
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Difficulty:

15% (low)

Question Stats:

74% (01:54) correct 26% (00:35) wrong based on 114 sessions

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How many hours did it take Helen to drive from her house to her parent's house?

(1) Helen's average speed on this trip was 72 kilometers per hour
(2) If Helen's average speed on this trip had been 8 kilometers per hour greater , it would have taken her 1 hour less.

OPEN DISCUSSION OF THIS QUESTION IS HERE: how-many-hours-did-it-take-helen-to-drive-from-her-house-to-91891.html
[Reveal] Spoiler: OA

Last edited by Bunuel on 30 Aug 2013, 04:08, edited 1 time in total.
Moved to DS forum and added the OA.
Manager
Joined: 03 Jun 2008
Posts: 137
Schools: ISB, Tuck, Michigan (Ross), Darden, MBS

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23 Jul 2008, 22:58
Statement 1: Alone is insufficient as distance is unavailable.

Statement 2: Alone is insufficient as neither speed nor distance is available.

Combining Both: From Statement 1 we know that 72 km/hr is the avg. speed. Let the time taken by helen be X.

Thereforhome.e distance travelled by Helen is 72*X

From statement 2, we know that if the speed had been 8 km/hr more than the original it would take 1 hr less.

=> 72X/80 = X-1

Therefore we can solve for X, which is the time take by Helen.
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Manager
Joined: 14 Jun 2008
Posts: 161

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24 Jul 2008, 03:55
(1) cannot say anything

Let x = time taken in 72 km / hr case

since distance = speed * time

72x = (72 + 8) (x -1)
72x = 80(x - 1)
8x = 80
x = 10

so (2) sufficient

so B
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Joined: 28 Dec 2004
Posts: 3357
Location: New York City
Schools: Wharton'11 HBS'12

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24 Jul 2008, 04:05
djdela wrote:
How many hours did it take Helen to drive from her house to her parent's house?

(1) Helen's average speed on this trip was 72 kilometers per hour
(2) If Helen's average speed on this trip had been 8 kilometers per hour greater , it would have taken her 1 hour less.

i suck at Q..what can i say..

D/V=t

D/(v+8)=t+1

Vt=(t+1)(v+8)
vt+8t+v=vt

8t+v=0...we dont know V and and t..

1) we are told v=72

1+2) 8t=72 t=9

i get C..
Manager
Joined: 14 Jun 2008
Posts: 161

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24 Jul 2008, 04:10
sset009 wrote:
(1) cannot say anything

Let x = time taken in 72 km / hr case

since distance = speed * time

72x = (72 + 8) (x -1)
72x = 80(x - 1)
8x = 80
x = 10

so (2) sufficient

so B

oops used, info from 1
should be C
Senior Manager
Joined: 19 Mar 2008
Posts: 351

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24 Jul 2008, 08:45
How many hours did it take Helen to drive from her house to her parent's house?

(1) Helen's average speed on this trip was 72 kilometers per hour
(2) If Helen's average speed on this trip had been 8 kilometers per hour greater , it would have taken her 1 hour less.

(1) alone is NOT sufficient. it just gives speed, no information on time and distance.

(2) alone is NOT sufficient. We can derive a relationship: (let x be speed, t = time)
x*t = (x+8)*(t-1)

(1) +(2), then 72t = 80(t-1)
Sufficient

Ans is C
Manager
Joined: 07 May 2013
Posts: 109
Re: How many hours did it take Helen to drive from her house to [#permalink]

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29 Aug 2013, 21:01
D/72-D/80=1
solve for D. we get D=720
Math Expert
Joined: 02 Sep 2009
Posts: 39695
Re: How many hours did it take Helen to drive from her house to [#permalink]

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30 Aug 2013, 04:08
OPEN DISCUSSION OF THIS QUESTION IS HERE: how-many-hours-did-it-take-helen-to-drive-from-her-house-to-91891.html
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Re: How many hours did it take Helen to drive from her house to   [#permalink] 30 Aug 2013, 04:08
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