RTD DS From Thursdays with Ron 4/29/2010

[amo6figs]

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.

[gokul_nair1984]

This should help you out....

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

[amo6figs]

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.

[gokul_nair1984]

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!

[tim]

:)