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GMATPrep - 400KM in the wrong lane

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Source: — Data Sufficiency |
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by jasonc » Sat May 31, 2008 5:20 pm
1) insuff. Tells us nothing about speed (could be different in the first vs second 200km)

2) gives us the following equation:
(r1+20) t2 = 400km
(r1)(t1) = 400km
t2-t1 = 1 hour

3 equations, 3 unknowns = suff.
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by AleksandrM » Sat May 31, 2008 7:01 pm
jason,

you've exposed a pretty major flaw in my approach to DS problems. I often focus too much on actually solving the problem, rather than just getting enough information to show me that there is enough info to get the answer.

Sometimes, I have to go through more elaborate steps when dealing with number properties, but for the most part I should really focus on just establishing sufficiency and saving 30 or 40 seconds here and there.
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by jasonc » Sat May 31, 2008 7:13 pm
yes, your time management should improve drastically once you start solving for sufficiency instead of actual numbers.

I use to suffer from the same issue. I recommend going through all of the OG11's DS questions, if you learn to solve them all in under 2 min, you'll learn many tricks to apply to different DS questions to solve for sufficiency.
I beat the GMAT! 760 (Q49/V44)
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by airan » Sun Jun 01, 2008 12:39 am
It can be done with 2 equations also.
Let the speed be s and time be t.

400/s=t

400/s+2= = t-1, so 2 equations with 2 variables. can be solved.
Answer is B
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