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robertpatrick
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 Posted: Tue Jul 15, 2008 9:21 pm Post subject: Error in OG 11? |
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Page 59, solution for problem #33
The question is: Is 5^(x+2) / 25 < 1?
1. 5^(x) < 1
2. x < 0
I put choice B because I knew from the stem that 5^(x) < 1 already, there's no new information in number 1.
The right answer is supposed to be D, and I can see how they could both be individually sufficient, 1 being always false and 2 being always true...
But to me this is like having a question like:
Is x < 1?
1. x <1> 0 |
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Ian Stewart
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| Posted: Wed Jul 16, 2008 8:46 am Post subject: Re: Error in OG 11? |
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| robertpatrick wrote: | I put choice B because I knew from the stem that 5^(x) < 1 already, there's no new information in number 1.
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You don't know anything at all from the stem- it doesn't state any facts, just asks a question. I don't quite follow your logic, but it appears that you are assuming that the inequality in the stem is true. You cannot assume that- that's the question you need to answer. |
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robertpatrick
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| Posted: Wed Jul 16, 2008 12:08 pm Post subject: |
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Thank you Ian, I see what you mean.
It was a little late last night.. |
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ildude02
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| Posted: Fri Jul 18, 2008 9:44 am Post subject: Re: Error in OG 11? |
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| Ian Stewart wrote: | | robertpatrick wrote: | I put choice B because I knew from the stem that 5^(x) < 1 already, there's no new information in number 1.
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You don't know anything at all from the stem- it doesn't state any facts, just asks a question. I don't quite follow your logic, but it appears that you are assuming that the inequality in the stem is true. You cannot assume that- that's the question you need to answer. |
But if the question(after reducing it) asks for if "5 ^ X < 1" and if the supporting statement says so, then why shouldn't we pick A as sufficient ? I'm confused, can you please explain what might be the reason we can't say that statement 1 is SUFFICIENT? |
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Stuart Kovinsky
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| Posted: Fri Jul 18, 2008 11:16 am Post subject: Re: Error in OG 11? |
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| ildude02 wrote: | | Ian Stewart wrote: | | robertpatrick wrote: | I put choice B because I knew from the stem that 5^(x) < 1 already, there's no new information in number 1.
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You don't know anything at all from the stem- it doesn't state any facts, just asks a question. I don't quite follow your logic, but it appears that you are assuming that the inequality in the stem is true. You cannot assume that- that's the question you need to answer. |
But if the question(after reducing it) asks for if "5 ^ X < 1" and if the supporting statement says so, then why shouldn't we pick A as sufficient ? I'm confused, can you please explain what might be the reason we can't say that statement 1 is SUFFICIENT? |
We CAN say that (1) is sufficient, that's why (b), which the OP chose, isn't the correct answer.
Robertpatrick started out great by simplifying the question, something that often makes life easier in DS. We can definitely reduce the question to:
is 5^x < 1?
However, Robertpatrick took that as information, rather than a question, and decided that (1) was insufficient because it just repeated what we already knew. Whenever a statement gives absolutely no new information (which is rare, but does happen sometimes on the GMAT), we immediately know that the statement is insufficient (and can also eliminate the "together" choice).
Here's an example:
If Bob drove from town A to town C at 20 mph, how long did the trip take?
(1) If Bob had driven at 10 miles per hour, it would have taken him twice as long.
Well, (1) might seem like useful information, but it's actually worthless, since it reduces to: "if you halve your speed, you double your time", which we can derive from the d=rt equation itself. If you faced this question on test day, you'd immediately elminiate (a), (c) and (d).
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ildude02
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| Posted: Fri Jul 18, 2008 11:24 am Post subject: |
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| Thanks for the explanation. |
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saeed
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| Posted: Fri Jul 18, 2008 12:47 pm Post subject: |
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Sorry guys i cant follow anyone's logic.Stuart has given a nice explanation. But my point is that, in his explanation he has compare two different questions type, one is y/n and the other is value question. Definitely, we can reduce the question stem into- Is 5^x<1?
so its a y/n question. That means we have nothing to assume & the question doesn't give any extra information. But the statement 1 is saying that 5^x<1. So, it gives a yes answer to the question. So it is sufficient. Statement two says that X is negative. So it is also giving the answer. So the answer should be D. Stuart please help me to identify the error of my reasoning. |
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robertpatrick
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| Posted: Fri Jul 18, 2008 2:05 pm Post subject: |
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| Choice D is right, Stuart explained what was going on when I did the question better than I did! That was exactly my thought process. |
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