Marla from OG Preptest

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drhomler: Master | Next Rank: 500 Posts; Posts: 141; Joined: Thu May 03, 2007 1:15 pm

by drhomler » Sat Jun 16, 2007 6:05 am

During a 40 mile trip Marla traveled at an average speed of x miles per hour for the first y miles of the trip and at an average rate of 1.25x miles per hour for the last 40-y miles of the trip. The time that Marla took to travel the 40 miles was what percent of the time it would have taken her if she had traveled at an average rate ox x miles per hour for the entire trip.

1)x=48
2)y=20

OA in a little bit. This one really got me I still dont understnad why the anser is what it is.

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Source: Beat The GMAT — Data Sufficiency | Sat Jun 16, 2007 6:05 am

goutamn: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Mon Apr 30, 2007 7:14 am

by goutamn » Sat Jun 16, 2007 8:44 am

is the ans a?

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jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

by jayhawk2001 » Sat Jun 16, 2007 9:01 am

Total time = y/x + (40-y)/1.25x = (0.25y + 40)/1.25x

Total time if Marla traveled at x mph = 40/x

Ratio = (0.25y + 40) / 1.25*40

From this we can see that y alone is sufficient to answer the ratio
question.

1 - insufficient.

2 - sufficient.

Is it B ?

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drhomler: Master | Next Rank: 500 Posts; Posts: 141; Joined: Thu May 03, 2007 1:15 pm

by drhomler » Sat Jun 16, 2007 9:08 am

Jay spot on as always-this one really threw me for a loop. I tried to set up a table and plug in x and y and set them equal and all that jazz. Do you think the best way to do these is just put the algebra together and go from there? I always want to plug in numbers.

OA is B

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jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

by jayhawk2001 » Sat Jun 16, 2007 9:20 am

drhomler wrote:Jay spot on as always-this one really threw me for a loop. I tried to set up a table and plug in x and y and set them equal and all that jazz. Do you think the best way to do these is just put the algebra together and go from there? I always want to plug in numbers.

OA is B

I'd suggest using the method you are most comfortable with. If you have
had a higher % of success using tables, you should see how you can
use that to your advantage.

For me, equations work better (as I suck at tables

).

For this particular problem, I'd recommend equations as the
problem clearly asks for a ratio (and you know GMAT is tricking
you into believing that you need both x and y to solve this

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