I know this DS problem from a CAT exam has been addressed in a previous thread. However, I do not understand the way that this problem is explained in the 'Solution' section of the CAT exam. Please help break the problem down into more understandable terms.
Bob and Wendy planned to walk from their home to a restaurant for dinner together. However, Bob was delayed at work, and Wendy left for the restaurant before Bob did. If the restaurant is 3 miles from their home and Bob left for the restaurant a half-hour after Wendy did, how long did Wendy have to wait for Bob at the restaurant?
(1) Wendy walked at a constant pace of 4 miles per hour
(2) Bob walked at a constant pace of 1 mile per hour faster than Wendy.
ANSWER: C: Both statements TOGETHER are sufficient, but NEITHER one ALONE is sufficient.
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- agalstia
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- mschwrtz
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Re: Bob and Wendy planned to walk from their home to a...
agalstia, post explanation, point to the what you find troublesome. I'd hate to answer your question with an account just as mystifying as the one one you've already found unsatisfactory.
In the meantime, a few points:
-What you need to know is THE DIFFERENCE BETWEEN THE TIME IT TOOK BOB TO WALK THREE MILES AND THE TIME IT TOOK WENDY TO WALK THREE MILES. If you know that, you can figure out how long Wendy had to wait. For instance, if Wendy's traveling time is 2 minutes less than Bob's, then she'll wait for 32 minutes (30+2). If Bob's travel time is 2 minutes less than Wendy's, then she'll wait for 28 minutes (30-2).
-If within 20 seconds or so you don't see this opportunity to rephrase the question AND you can't see how to start translating from English into algebra, make a RTD table.
-S1 doesn't tell you anything about Bob.
-S2 is also not sufficient. You can see this by trying particular speeds 1 mph apart (3 mph and 4 mph give you a 15-minute difference, while 4 mph and 5 mph give you a 12-minute difference), by thinking about extreme cases (as Wendy's speed approaches 0, the difference approaches infinity, as Wendy's speed approaches infinity, the difference approaches 0), or by doing algebra.
-One way to represent S2 algebraically would be to call Wendy's rate r and Bob's rate r+1. This allows us to rephrase the questions as "[3/(r+1)]-(3/r)=?" Since the expression 3/(r+1)]-(3/r) represents no unique constant value, S2 is insufficient.
In the meantime, a few points:
-What you need to know is THE DIFFERENCE BETWEEN THE TIME IT TOOK BOB TO WALK THREE MILES AND THE TIME IT TOOK WENDY TO WALK THREE MILES. If you know that, you can figure out how long Wendy had to wait. For instance, if Wendy's traveling time is 2 minutes less than Bob's, then she'll wait for 32 minutes (30+2). If Bob's travel time is 2 minutes less than Wendy's, then she'll wait for 28 minutes (30-2).
-If within 20 seconds or so you don't see this opportunity to rephrase the question AND you can't see how to start translating from English into algebra, make a RTD table.
-S1 doesn't tell you anything about Bob.
-S2 is also not sufficient. You can see this by trying particular speeds 1 mph apart (3 mph and 4 mph give you a 15-minute difference, while 4 mph and 5 mph give you a 12-minute difference), by thinking about extreme cases (as Wendy's speed approaches 0, the difference approaches infinity, as Wendy's speed approaches infinity, the difference approaches 0), or by doing algebra.
-One way to represent S2 algebraically would be to call Wendy's rate r and Bob's rate r+1. This allows us to rephrase the questions as "[3/(r+1)]-(3/r)=?" Since the expression 3/(r+1)]-(3/r) represents no unique constant value, S2 is insufficient.
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