Error in OG 11?

BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

This topic has expert replies

Post new topic Post Reply

Previous Topic Next Topic

robertpatrick: Senior | Next Rank: 100 Posts; Posts: 39; Joined: Mon Jul 07, 2008 8:13 pm; Thanked: 1 times

Error in OG 11?

by robertpatrick » Tue Jul 15, 2008 8:21 pm

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

Quote

Source: Beat The GMAT — Data Sufficiency | Tue Jul 15, 2008 8:21 pm

GMAT/MBA Expert

Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 am; Location: Montreal; Thanked: 1090 times; Followed by:355 members; GMAT Score:780

Re: Error in OG 11?

by Ian Stewart » Wed Jul 16, 2008 7:46 am

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.

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.

Quote

robertpatrick: Senior | Next Rank: 100 Posts; Posts: 39; Joined: Mon Jul 07, 2008 8:13 pm; Thanked: 1 times

by robertpatrick » Wed Jul 16, 2008 11:08 am

Thank you Ian, I see what you mean.
It was a little late last night..

Quote

ildude02: Master | Next Rank: 500 Posts; Posts: 320; Joined: Sun Jan 13, 2008 10:00 pm; Thanked: 10 times

Re: Error in OG 11?

by ildude02 » Fri Jul 18, 2008 8:44 am

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.
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?

Quote

Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pm; Location: Toronto; Thanked: 1710 times; Followed by:614 members; GMAT Score:800

Re: Error in OG 11?

by Stuart@KaplanGMAT » Fri Jul 18, 2008 10:16 am

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.
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).

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course

Quote

ildude02: Master | Next Rank: 500 Posts; Posts: 320; Joined: Sun Jan 13, 2008 10:00 pm; Thanked: 10 times

by ildude02 » Fri Jul 18, 2008 10:24 am

Thanks for the explanation.

Quote

saeed: Junior | Next Rank: 30 Posts; Posts: 23; Joined: Tue Nov 27, 2007 9:40 pm

by saeed » Fri Jul 18, 2008 11:47 am

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.