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How many hours did it take Helen to drive from her house to her parent [#permalink]

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26 Mar 2010, 17:00

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A

B

C

D

E

Difficulty:

25% (medium)

Question Stats:

76% (01:44) correct
24% (00:41) wrong based on 341 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.

How many hours did it take Helen to drive from her house to her parent [#permalink]

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26 Mar 2010, 17:10

Expert's post

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changhiskhan wrote:

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

Thanks in advance!

\(d=rt\), where \(d\) is the distance covered, \(r\) rate and \(t\) time. Question: \(t=?\)

(1) \(r=72\). Clearly not sufficient. (2) \((r+8)(t-1)=d\). Clearly not sufficient.

Re: How many hours did it take Helen to drive from her house to her parent [#permalink]

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27 Mar 2010, 08:52

changhiskhan wrote:

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

Thanks in advance!

1: Not sufficient, easy to spot 2: distance is d av speed: a then time is t av speed: a-1 then time is t-1 d/a = d/a+8 + 1 can't solve alone insufficient.

Combining, d/72 = d/80 + 1 solving d = 80 then t can be calculated hence C.

Re: How many hours did it take Helen to drive from her house to her parent [#permalink]

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27 Apr 2010, 05:57

zz0vlb wrote:

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

(1) Helen's average speed on this trip was 72 km/hr. (2) If Helen's average speed on this trip has been 8 km/hr greater, it would have taken her 1 hour less.

Re: How many hours did it take Helen to drive from her house to her parent [#permalink]

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15 Mar 2011, 23:39

1

This post received KUDOS

changhiskhan wrote:

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

Thanks in advance!

C after 3:40 minutes _________________

Consider giving me kudos if you find my explanations helpful so i can learn how to express ideas to people more understandable.

Re: How many hours did it take Helen to drive from her house to her parent [#permalink]

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26 Nov 2012, 07:38

Could you also solve this problem by thinking of it as a ratio? One of MGMAT's strategies for DS ratio questions is that if a DS question asks for the concrete value of one element of a ratio, you will need both the concrete value of another element and the relative value of 2 elements of the ratio. When you combine the two statements, you get a concrete value from statement 1 and two relative values from statement 2. Is that a logical way to solve this problem, once you already know that the two statements individually are insufficient? _________________

Advice, Musings, and Experiences from a member of the HBS Class of 2016 http://DefyingGravityMBA.blogspot.com/

Re: How many hours did it take Helen to drive from her house to her parent [#permalink]

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01 Aug 2013, 11:52

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

1) Helen’s average speed on this trip was 72 kilometers per hour. We know nothing about distance. If the distance was 72km then it would have taken one hour. If the distance was 720km then it would have taken 10 hours, etc. All we know is r=72 INSUFFICIENT

2) If Helen’s average speed on this trip had been 8 kilometers per hour greater, it would have taken her 1 hour less. Time=distance/speed T-1 = d/(s+8) This does not provide enough information to solve for the question. INSUFFICIENT

1+2) average speed (r) = 72, t-1 = d/(s+8) t-1 = d/(72+8) t-1 = d/80 This is where it gets tricky. At first I said that this isn't enough information to solve so I put down (E). However, d=r*t. If I plug in for d then I can cancel out t leaving r. t-1 = r*t/(72+8) t-1 = 72*t/(80) 80t-80 = 72t 8t = 80 t=10

A couple things to remember: - If in doubt and unable to solve, try and substitute in a formula (like=r*t) to cancel out variables. - remember to plug in any applicable numbers for all variables. For example, after plugging in r*t for d, I forgot to plug in 72 for r*t. SUFFICIENT

Re: How many hours did it take Helen to drive from her house to her parent [#permalink]

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13 Oct 2014, 21:16

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: How many hours did it take Helen to drive from her house to her parent [#permalink]

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17 Nov 2014, 11:29

PTK wrote:

basically, we are provided with two equations in 1statement 1 and 2. having two equations it is possible to solve equality with two uknowns.

hence it is C.

30 seconds.

Well, I thought that we were provided with 3 equations and 3 variables. The answer is the same (C) but I think my reasoning is slightly different.

Question stem: RT = D (3 variables, 1 equation). We need 2 more equations in the statements to solve this problem. Remember, whenever you are dealing with distance, you already have an equation (RT = D). The same goes for Work Problems (RT = W)

St 1: R = 72. Insufficient. St 1 just gives us 1 more equation.

St. 2: (R + 8)(T - 1) = D. Insufficient. St 2 just gives us 1 more equation.

St 1 + 2: we now have 2 more equations apart from the one given in the question stem. We now have 3 equations and 3 unknowns. We can solve for this stuff: no need to do the calculations.

Hope it makes sense. _________________

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Re: How many hours did it take helen to drive from her house to [#permalink]

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21 Sep 2015, 22:39

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: How many hours did it take Helen to drive from her house to her parent [#permalink]

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22 Sep 2015, 07:07

WholeLottaLove wrote:

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

1) Helen’s average speed on this trip was 72 kilometers per hour. We know nothing about distance. If the distance was 72km then it would have taken one hour. If the distance was 720km then it would have taken 10 hours, etc. All we know is r=72 INSUFFICIENT

2) If Helen’s average speed on this trip had been 8 kilometers per hour greater, it would have taken her 1 hour less. Time=distance/speed T-1 = d/(s+8) This does not provide enough information to solve for the question. INSUFFICIENT

1+2) average speed (r) = 72, t-1 = d/(s+8) t-1 = d/(72+8) t-1 = d/80 This is where it gets tricky. At first I said that this isn't enough information to solve so I put down (E). However, d=r*t. If I plug in for d then I can cancel out t leaving r. t-1 = r*t/(72+8) t-1 = 72*t/(80) 80t-80 = 72t 8t = 80 t=10

A couple things to remember: - If in doubt and unable to solve, try and substitute in a formula (like=r*t) to cancel out variables. - remember to plug in any applicable numbers for all variables. For example, after plugging in r*t for d, I forgot to plug in 72 for r*t. SUFFICIENT

(C)

Thanks, that was very helpful.

I chose E and was having a hard time figuring out other people's explanations.

gmatclubot

Re: How many hours did it take Helen to drive from her house to her parent
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22 Sep 2015, 07:07

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