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knight247: Legendary Member; Posts: 504; Joined: Tue Apr 19, 2011 1:40 pmFollowed by: 11 members; Thanked: 114 times

by knight247 » Thu Jun 23, 2011 10:45 am

How many numbers 'n' are there whose units digit is 2?
(1)n is a 5-digit number so that no two digits are repeated.
(2)n is divisible by 2.

(A)Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked.
(B)Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked.
(C)BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient.
(D)EACH statement ALONE is sufficient to answer the question asked.
(E)Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data are needed.

Detailed explanations would be appreciated

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Source: Beat The GMAT — Data Sufficiency | Thu Jun 23, 2011 10:45 am

Frankenstein: Legendary Member; Posts: 1448; Joined: Tue May 17, 2011 9:55 amFollowed by: 53 members; Location: India; Thanked: 375 times

by Frankenstein » Thu Jun 23, 2011 11:16 am

Hi,
From(1):
_,_,_,_,2
We know that we can count the numbers. we do not really count them.
But, if you want to count
1st digit can be picked from 1to9 except 2 in 8 ways
2nd in 8 ways
3rd in 7 ways
4th in 6ways
So, total = 8.8.7.6ways
Sufficient
From(2):n is divisible by 2
We do not know the number of digits in n. So we can find infinitely many such numbers
Not sufficient

Hence, A

Cheers!

Things are not what they appear to be... nor are they otherwise

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

by Ian Stewart » Thu Jun 23, 2011 12:43 pm

This question makes no logical sense. From Statement 1, we learn that there are some restrictions on what n can be, but we have no idea if these are the *only* restrictions on the value of n. If they are, of course you can count how many n there are. If they are not, then of course you can't without more information. There's no way to guess which case is which unless you have some psychic connection with the question writer. The format of the question is simply illogical. Where is it from?

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knight247: Legendary Member; Posts: 504; Joined: Tue Apr 19, 2011 1:40 pmFollowed by: 11 members; Thanked: 114 times

by knight247 » Thu Jun 23, 2011 9:45 pm

This is from the GMAT study books of a coaching institute here in Mumbai. This particular question is listed as a 'very hard' problem.

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Frankenstein: Legendary Member; Posts: 1448; Joined: Tue May 17, 2011 9:55 amFollowed by: 53 members; Location: India; Thanked: 375 times

by Frankenstein » Thu Jun 23, 2011 9:51 pm

Hi,
Can you post OA in spoiler or at least after some discussions for all the questions you post.

Cheers!

Things are not what they appear to be... nor are they otherwise

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knight247: Legendary Member; Posts: 504; Joined: Tue Apr 19, 2011 1:40 pmFollowed by: 11 members; Thanked: 114 times

by knight247 » Fri Jun 24, 2011 12:14 am

Hey Frank,
Actually i don't have the OA for this or the other 4 DS questions i posted. Sorry man.

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

by Ian Stewart » Fri Jun 24, 2011 1:57 am

knight247 wrote:This is from the GMAT study books of a coaching institute here in Mumbai. This particular question is listed as a 'very hard' problem.

Sure, it's 'very hard', because it's impossible to tell what it means. It's easy to invent 'very hard' problems - for example, I could ask "What prime number am I thinking of?" That's a hard problem for anyone (but me) to get right, but it's certainly not a good practice problem. The same is true of several of the questions you've posted recently on this forum, which I guess must be from the same coaching institute - they're badly written, make next to no logical sense, and often have the wrong answer. If you're preparing for the GMAT, you absolutely should find higher quality materials to study from, because you're just wasting your time with this institute's material. Even using only the questions posted to this forum by other participants you'll get much better practice than you're getting from studying questions like the one above.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com

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