GMATPrep DS 33

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parisfr67: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Sun Jan 27, 2008 3:25 pm; Location: Toronto

by parisfr67 » Mon Jan 28, 2008 5:34 pm

Question comes from GMATPrep#1 DS#33 -- See attached file for question

what is the val for p?
(1) p/4 is PRIME ...
PRIME are 2,3,5,7,11,13,17,19, etc ... having no factor except itself and one .. How can anything be divided by four and be a prime number .. NOT SUFF

(2) p is divisible by 3 ... Many numbers divisible by 3 ... NOT SUFF

Together:
p is div by 3 and p/4 is PRIME ... I see a contradiction with the definition of prime numbers ... Hence my answer of E

Correct Answer is C ... Can someone explain to me how p/4 is PRIME given p is divisible by 3

regards
Alain

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Source: Beat The GMAT — Data Sufficiency | Mon Jan 28, 2008 5:34 pm

stellategang: Junior | Next Rank: 30 Posts; Posts: 15; Joined: Mon Oct 29, 2007 12:43 pm; Thanked: 2 times

Re: GMATPrep DS 33

by stellategang » Mon Jan 28, 2008 6:52 pm

parisfr67 wrote: what is the val for p?
(1) p/4 is PRIME ...
PRIME are 2,3,5,7,11,13,17,19, etc ... having no factor except itself and one .. How can anything be divided by four and be a prime number .. NOT SUFF

I think you're reading 1 incorrectly. Statement 1 is not saying that p is prime but that the expression (p/4) is a PRIME. So for example (28/4) = 7 is prime (i.e. 7) but notice that (12/4) = 3 is a prime too (i.e. 3) . So in this interpretation 1 is INSUFF because (p/4) could equal 7 or 3 depending on p.

(2) p is divisible by 3 ... Many numbers divisible by 3 ... NOT SUFF

TRUE

Together:
p is div by 3 and p/4 is PRIME ... I see a contradiction with the definition of prime numbers ... Hence my answer of E

Correct Answer is C ... Can someone explain to me how p/4 is PRIME given p is divisible by 3

The only value for p where the expression (p/4) is prime AND p is divisible by three is the value of 12, where p = 12.

ANSWER IS C

hope that helps? . . . looks like you just misread statement 1?

regards
Alain

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

by Stuart@KaplanGMAT » Tue Jan 29, 2008 10:58 am

Stellategang evaluated your situation perfectly - you've completely misinterpreted both the question and statement (1).

A good tip for test day is that if you look at a statement and it seems like it's impossible, then you KNOW that you've misinterpreted something. "Impossible" is NOT the same thing as "insufficient".

In fact, NO statement on the GMAT will lead to an impossible situation. There has to be at least one solution to every question asked.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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