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challenge question 10/21/02

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jigar24
 Post subject: challenge question 10/21/02
 Post Posted: Tue Oct 26, 2010 10:13 pm 
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Students


Posts: 57
Question
Train A leaves New York for Boston at 3 PM and travels at the constant speed of 100 mph. An hour later, it passes Train B, which is making the trip from Boston to New York at a constant speed. If Train B left Boston at 3:50 PM and if the combined travel time of the two trains is 2 hours, what time did Train B arrive in New York?

(1) Train B arrived in New York before Train A arrived in Boston.

(2) The distance between New York and Boston is greater than 140 miles.

How to solve this within 2 mins? I know solution is D but its impossible to prove step 1 sufficient within 2 mins.. Please suggest a short cut method
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mschwrtz
 Post subject: Re: challenge question 10/21/02
 Post Posted: Wed Oct 27, 2010 5:38 pm 
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ManhattanGMAT Staff


Posts: 506
Hmm....

It's not impossible, though I couldn't do it. I hadn't seen this question before, so I timed myself solving it. It took me about 90 seconds to determine from the question that the B-->NY train was going either 200 or 300 mph. If I hadn't known from your post that S1 was sufficient, I'm sure that it would have taken me at least 3:00 to do the whole question.

That's OK because:

(1) I can take a little extra time here if I've already banked it on earlier questions. For many students, getting a question right in much over three minutes is worse than getting it wrong under two minutes, but I don't have to be right at or under 2:00 on every question.

(2) This isn't a real GMAT question anyway. Those challenge bank questions are crazy hard. I can generally do 5 in 10 minutes, but if I try to sustain that pace for 20 or 30 minutes...whew. Not gonna happen.
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