DS Practice test question #15

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missionmba: Master | Next Rank: 500 Posts; Posts: 288; Joined: Thu Jul 31, 2008 10:54 pm; Location: Bombay, India

by missionmba » Fri Aug 29, 2008 6:41 am

DS Practice test question

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Mission Mba

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Source: Beat The GMAT — Data Sufficiency | Fri Aug 29, 2008 6:41 am

California4jx: Master | Next Rank: 500 Posts; Posts: 227; Joined: Thu Aug 14, 2008 10:43 amFollowed by: 1 member; Thanked: 7 times; GMAT Score:650

by California4jx » Fri Aug 29, 2008 8:18 am

It should be A -

let me know OA - then I'll explain

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II: Master | Next Rank: 500 Posts; Posts: 400; Joined: Mon Dec 10, 2007 1:35 pm; Location: London, UK; Thanked: 19 times; GMAT Score:680

by II » Fri Aug 29, 2008 2:27 pm

My answer to this is C. See explanation below

First ANALYSE the QUESTION STEM. In particular note that there is no information given about p or r. They can be negative numbers, they can be fractions etc ... it doesnt say anything about them being positives or integers.
If you dont take note of this you can fall into choosing the trap answer A.

Also note that the inequality can be simplified:
1/p > r/(r^2 + 2)
1/p > r/(rr+2)
1/p > 1/(r+2)

(1) p = r
so lets replace the r with p in the inequalty 1/p > 1/(r+2)
This becomes to: 1/p > 1/(p+2)

It would appear that this would provide SUFF information to solve, but lets double check by considering 2 scenarios:
1) let p = positive fraction... say 1/4.
so we have: 1/(1/4) > 1/(1/4 + 2)
becomes: 4 > 4/9 ... and we can answer YES to this question. 4 is greater than a 4/9.
2) let p = negative fraction ... say -(1/4).
so we have 1/-(1/4) > 1/(-(1/4)+2)
this becomes -4 > 4/7 ... and we can answer NO to this question. -4 is NOT greater than 4/7.

So hence (1) is INSUFF to answer the question.

(2) r>0 is INSUFF since it provide no details about p.

(1) and (2) together is SUFF because statement (2) rules out the possibility of the negative values (in our example the negative fraction).

So I guess the key take-away from this is to make a note of what info IS provided in q-stem and what is NOT provided.

But then again ... I may be totally wrong here ... whats the official answer here?

Thanks.
II

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parallel_chase: Legendary Member; Posts: 1153; Joined: Wed Jun 20, 2007 6:21 amFollowed by: 2 members; Thanked: 146 times

by parallel_chase » Fri Aug 29, 2008 2:40 pm

I agree with II answer has to be C. I'll be really surprised if the answer is E.

Since r>0 => 1/r > r/r^2+2

Whats the OA?

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missionmba: Master | Next Rank: 500 Posts; Posts: 288; Joined: Thu Jul 31, 2008 10:54 pm; Location: Bombay, India

by missionmba » Sat Aug 30, 2008 12:58 am

II wrote:My answer to this is C. See explanation below

First ANALYSE the QUESTION STEM. In particular note that there is no information given about p or r. They can be negative numbers, they can be fractions etc ... it doesnt say anything about them being positives or integers.
If you dont take note of this you can fall into choosing the trap answer A.

Also note that the inequality can be simplified:
1/p > r/(r^2 + 2)
1/p > r/(rr+2)
1/p > 1/(r+2)

(1) p = r
so lets replace the r with p in the inequalty 1/p > 1/(r+2)
This becomes to: 1/p > 1/(p+2)

It would appear that this would provide SUFF information to solve, but lets double check by considering 2 scenarios:
1) let p = positive fraction... say 1/4.
so we have: 1/(1/4) > 1/(1/4 + 2)
becomes: 4 > 4/9 ... and we can answer YES to this question. 4 is greater than a 4/9.
2) let p = negative fraction ... say -(1/4).
so we have 1/-(1/4) > 1/(-(1/4)+2)
this becomes -4 > 4/7 ... and we can answer NO to this question. -4 is NOT greater than 4/7.

So hence (1) is INSUFF to answer the question.

(2) r>0 is INSUFF since it provide no details about p.

(1) and (2) together is SUFF because statement (2) rules out the possibility of the negative values (in our example the negative fraction).

So I guess the key take-away from this is to make a note of what info IS provided in q-stem and what is NOT provided.

But then again ... I may be totally wrong here ... whats the official answer here?

Thanks.
II

Hey this part is not right
-------------------------------------
Also note that the inequality can be simplified:
1/p > r/(r^2 + 2)
1/p > r/(rr+2)
1/p > 1/(r+2)
-------------------------------------

it will become
1/p > 1/(r + {2/r})

Mission Mba

Everyone has a will to win but very few have the will to prepare to win

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II: Master | Next Rank: 500 Posts; Posts: 400; Joined: Mon Dec 10, 2007 1:35 pm; Location: London, UK; Thanked: 19 times; GMAT Score:680

by II » Sat Aug 30, 2008 7:02 am

whats the OA ?

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