Official Guide DS #163

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Nadia222: Senior | Next Rank: 100 Posts; Posts: 78; Joined: Sun Sep 15, 2013 8:38 amFollowed by: 6 members; Thanked: 8 times

by Nadia222 » Fri Jan 03, 2014 2:23 am

Hi,

I have a question in regards to Official Guide 13
Data Sufficiency questions 67 and 163.

I chose d for both questions but for question
67, d was incorrect because the quadratic allowed
For two possible answer choices,but for question 167 the correct
approach is to drop the negative quadratic (-10)
and leave the positive 15. If so why couldn't the same be done
for question 67. They are both value DS questions
regarding quadractics.

I'm not sure if I am allowed to post the questions, so I will not.
Any help will be greatly appreciated.

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Source: Beat The GMAT — Data Sufficiency | Fri Jan 03, 2014 2:23 am

theCodeToGMAT: Legendary Member; Posts: 1556; Joined: Tue Aug 14, 2012 11:18 pmFollowed by: 34 members; Thanked: 448 times; GMAT Score:650

by theCodeToGMAT » Fri Jan 03, 2014 8:03 am

Nadia, Please post the questions, one per thread; it's a public forum

R A H U L

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ceilidh.erickson: GMAT Instructor; Posts: 2095; Joined: Tue Dec 04, 2012 3:22 pmFollowed by: 247 members; Thanked: 1443 times

by ceilidh.erickson » Mon Jan 06, 2014 4:15 pm

Hi Nadia,

The OG is copyrighted material, but I think you'll find that you won't get in trouble for posting the actual question.

Rahul, you're right that generally people should post one comment per thread, but I think it's certainly reasonable to compare two similar questions, and ask what distinguishes them.

The biggest distinction between #67 and #163 is that 163 has an POSITIVE CONSTRAINT, and 67 does not.

#67: "What is the value of integer n?"
Here, n can be any integer, positive of negative - there's no restriction. When given n(n + 1) = 6, n could equal 2 or -3, and the statement is thus insufficient.

#163 "How many members does the club have?"
When you're dealing with a word problem that involves real-life, countable objects (people, books, cars, etc), there is an implied POSITIVE CONSTRAINT. We can't have a negative number of people! Thus, when the quadratic gives us -10 or 15, we know that the number of members cannot be negative, so it must be 15.

Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education

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Nadia222: Senior | Next Rank: 100 Posts; Posts: 78; Joined: Sun Sep 15, 2013 8:38 amFollowed by: 6 members; Thanked: 8 times

by Nadia222 » Thu Jan 09, 2014 5:55 pm

Thanks Ceilidh!!

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