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How many hours did it take Helen to drive from her house to [#permalink]
26 Mar 2010, 16:00

00:00

A

B

C

D

E

Difficulty:

25% (low)

Question Stats:

78% (01:44) correct
21% (00:40) wrong based on 103 sessions

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.

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.

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.

Driving to Helen's house - DS problem [#permalink]
27 Apr 2010, 04:35

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: Driving to Helen's house - DS problem [#permalink]
27 Apr 2010, 04:57

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.

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 [#permalink]
26 Nov 2012, 06:38

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?
_________________

Re: How many hours did it take Helen to drive from her house to [#permalink]
01 Aug 2013, 10:52

1

This post received KUDOS

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)

gmatclubot

Re: How many hours did it take Helen to drive from her house to
[#permalink]
01 Aug 2013, 10:52