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How long did it take Betty to drive nonstop on a trip from [#permalink]
 14 Mar 2012, 15:19
Question Stats:
52% (01:00) correct
47% (00:50) wrong based on 4 sessions
How long did it take Betty to drive nonstop on a trip from her home to Denver, Colorado? (1) If Betty's average speed for the trip had been 1\frac{1}{2} times as fast, the trip would have taken 2 hours. (2) Betty's average speed for the trip was 50 miles per hour.
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Magoosh GMAT Instructor
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Hi, there. I'm happy to help with this. Prompt: How long did it take Betty to drive nonstop on a trip from her home to Denver, Colorado?To apply D = RT, we would have to know both the distance and the speed to find the time. Statement #1: If Betty's average speed for the trip had been 1 and 1/2 times as fast, the trip would have taken 2 hours.Let D be the distance, and R be her speed. What this is saying is: D = (1.5R)*2 = 3*R This implies T = D/R = 3 --- the trip took her 3 hours. Statement #1, by itself, is sufficient. Statement #2: Betty's average speed for the trip was 50 miles per hour.Well, we know the average speed, but we don't know where Betty lives --- we have no idea of the distance from her home to Denver. Since we know R and don't know D, we can't find T. Statement #2, by itself, is insufficient. Here's a similar DS question, for more practice: http://gmat.magoosh.com/questions/927When you submit your answer to that, the next page will have a complete video explanation. Does all this make sense? Please let me know if you have any questions. Mike 
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mikemcgarry wrote: Hi, there. I'm happy to help with this. Prompt: How long did it take Betty to drive nonstop on a trip from her home to Denver, Colorado?To apply D = RT, we would have to know both the distance and the speed to find the time. Statement #1: If Betty's average speed for the trip had been 1 and 1/2 times as fast, the trip would have taken 2 hours.Let D be the distance, and R be her speed. What this is saying is: D = (1.5R)*2 = 3*R This implies T = D/R = 3 --- the trip took her 3 hours. Statement #1, by itself, is sufficient. Statement #2: Betty's average speed for the trip was 50 miles per hour.Well, we know the average speed, but we don't know where Betty lives --- we have no idea of the distance from her home to Denver. Since we know R and don't know D, we can't find T. Statement #2, by itself, is insufficient. Here's a similar DS question, for more practice: http://gmat.magoosh.com/questions/927When you submit your answer to that, the next page will have a complete video explanation. Does all this make sense? Please let me know if you have any questions. Mike Hi, Should the above not be D = ( 2.5R)*2 = 3*R? doesnt '1.5 times as fast ' imply 2.5R?
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Sachin9 wrote: Hi,
Should the above not be D = (2.5R)*2 = 3*R? Doesn't '1.5 times as fast ' imply 2.5R? No, it doesn't. This is a very subtle verbal thing. Suppose I have some beginning speed V. If I have a speed that is 1.5 time faster than this, that's 1.5*V BUT, if the speed increases by 1.5 this value, then that's V + 1.5*V = 2.5*V Moving at a speed 1.5 faster than the original is not the same as increasing your speed by 1.5 times beyond what the original was. Does this distinction make sense? Mike
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mikemcgarry wrote: Sachin9 wrote: Hi,
Should the above not be D = (2.5R)*2 = 3*R? Doesn't '1.5 times as fast ' imply 2.5R? No, it doesn't. This is a very subtle verbal thing. Suppose I have some beginning speed V. If I have a speed that is 1.5 time faster than this, that's 1.5*V BUT, if the speed increases by 1.5 this value, then that's V + 1.5*V = 2.5*V Moving at a speed 1.5 faster than the original is not the same as increasing your speed by 1.5 times beyond what the original was. Does this distinction make sense? Mike Thanks Mike, I suppose this is how it should be If I have a speed that is 1.5 times faster than this, that's 2.5*V If I have a speed that is 1.5 times as fast as this, that's 1.5*V This is how we apply for percentage based concepts.. Is my understanding correct? Regards, Sachin
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Sachin9 wrote: Thanks Mike, I suppose this is how it should be
If I have a speed that is 1.5 times faster than this, that's 2.5*V
If I have a speed that is 1.5 times as fast as this, that's 1.5*V
Is my understanding correct? Dear Sachin We are getting into some really subtleties of grammar and phrasing here. If I have a speed that is 1.5 times as fast as V ----> that clearly should be 1.5*V If my speed was V, but increased by 1.5 this value ----> that clearly should be 2.5*V If I have a speed that is 1.5 times faster than V -----> not 100% percent clear, but I would say most people would interpret this as 1.5*V. The GMAT is always crystal clear in its phrasing. There is no way they would use this phrasing and expect you to come up with 2.5*V. Part of what is unusual about this conversation is we are talking about the increases of speed. Almost everyone compares speed by saying "n times faster." In real life, no one ever talks about percentage increase or decreases for speed. Let's change the subject to something like profits. You are perfectly correct ---- If I say "profits increased by 150%", that's 2.5 times the original profits. Does all this make sense? Mike
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mikemcgarry wrote: Sachin9 wrote: Thanks Mike, I suppose this is how it should be
If I have a speed that is 1.5 times faster than this, that's 2.5*V
If I have a speed that is 1.5 times as fast as this, that's 1.5*V
Is my understanding correct? Dear Sachin We are getting into some really subtleties of grammar and phrasing here. If I have a speed that is 1.5 times as fast as V ----> that clearly should be 1.5*V If my speed was V, but increased by 1.5 this value ----> that clearly should be 2.5*V If I have a speed that is 1.5 times faster than V -----> not 100% percent clear, but I would say most people would interpret this as 1.5*V. The GMAT is always crystal clear in its phrasing. There is no way they would use this phrasing and expect you to come up with 2.5*V. Part of what is unusual about this conversation is we are talking about the increases of speed. Almost everyone compares speed by saying "n times faster." In real life, no one ever talks about percentage increase or decreases for speed. Let's change the subject to something like profits. You are perfectly correct ---- If I say "profits increased by 150%", that's 2.5 times the original profits. Does all this make sense? Mike You Mike, It does Thanks a lot
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How long did it take Betty to drive nonstop on a trip from [#permalink]
21 Jan 2013, 02:34
alimad wrote: How long did it take betty to drive nonstop on a trip from her home to Denver, Colorado?
(1). If Betty's average speed for the trip had been 1 1/2 times as fast, the trip would have taken 2 hours.
(2). Betty's average speed for the trip was
50 miles / hour.
The distance is similar in this question equation 1 X be speed, t is the time and d is the distance X*t=d equation 2 1.5X*2=d >> 3X=d substitute in 1 x*t=3X t=3 is this approach correct?
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Re: How long did it take Betty to drive nonstop on a trip from [#permalink]
21 Jan 2013, 03:53
fozzzy wrote: alimad wrote: How long did it take betty to drive nonstop on a trip from her home to Denver, Colorado?
(1). If Betty's average speed for the trip had been 1 1/2 times as fast, the trip would have taken 2 hours.
(2). Betty's average speed for the trip was
50 miles / hour.
The distance is similar in this question equation 1 X be speed, t is the time and d is the distance X*t=d equation 2 1.5X*2=d >> 3X=d substitute in 1 x*t=3X t=3 is this approach correct? Yes, it is. Even without any formula: since moving 1.5 times as fast as the actual speed would take 2 hours to cover the distance, then moving at actual speed would take 2*1.5=3 hours to cover the same distance.
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Re: How long did it take Betty to drive nonstop on a trip from
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21 Jan 2013, 03:53
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