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RTD DS From Thursdays with Ron 4/29/2010

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amo6figs
 Post subject: RTD DS From Thursdays with Ron 4/29/2010
 Post Posted: Tue Oct 05, 2010 1:04 pm 
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Course Students


Posts: 2
Hope I have this in the right section, looking for help with the following DS question:

How much time did it take a certain car to travel 400 kilometers?

1) The car traveled the first 200 kilometers in 2.5 hours.

2) If the car's average speed had been 20 kilometers per hour greater than it was, it would have traveled the 400 kilometers in 1 hour less time than it did.

Answer is B.

I understand why 1) is insufficient, and I understand the structure for answering why 2) is sufficient.

What I need help with is working the algebra to bring the equation to a quadratic and solving for one negative and one positive answer. Could someone kindly walk me through the algebra?

Thanks in advance.
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gokul_nair1984
 Post subject: Re: RTD DS From Thursdays with Ron 4/29/2010
 Post Posted: Tue Oct 05, 2010 2:35 pm 
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Students


Posts: 170
This should help you out....

http://www.manhattangmat.com/forums/how-much-time-did-it-take-a-certain-car-to-travel-400-t348.html
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amo6figs
 Post subject: Re: RTD DS From Thursdays with Ron 4/29/2010
 Post Posted: Tue Oct 05, 2010 8:05 pm 
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Course Students


Posts: 2
gokul_nair1984 wrote:
This should help you out....

http://www.manhattangmat.com/forums/how-much-time-did-it-take-a-certain-car-to-travel-400-t348.html


GREAT find, thank you. For some reason it didn't show up in my original search. I forgot to cancel the "t" in the numerator and denominator from 400t-400/t + 20t=420.
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gokul_nair1984
 Post subject: Re: RTD DS From Thursdays with Ron 4/29/2010
 Post Posted: Tue Oct 05, 2010 9:11 pm 
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Students


Posts: 170
No Problems :) By the way try searching for the keyword on google and that might give you a better chance of returning the desired result. Good Luck!
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tim
 Post subject: Re: RTD DS From Thursdays with Ron 4/29/2010
 Post Posted: Fri Oct 08, 2010 1:08 am 
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ManhattanGMAT Staff


Posts: 2242
Location: Southwest Airlines, seat 21C
:)

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Tim Sanders
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