Is the sum of a series of n consecutive integers even?

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giovanni.gastone: Senior | Next Rank: 100 Posts; Posts: 51; Joined: Fri Feb 18, 2011 5:35 pm; Location: Florence, Italy

by giovanni.gastone » Sun May 22, 2011 8:56 pm

Source: Veritas

Is the sum of a series of n consecutive integers even?

(1) n=6
(2) The n digit number formed by the seriest is a multiple of nine

OA: A

Does anyone understand what the second statement is saying?

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Source: Beat The GMAT — Data Sufficiency | Sun May 22, 2011 8:56 pm

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

by Frankenstein » Sun May 22, 2011 9:12 pm

Hi,

From(1) : Lets the numbers be n,n+1,n+2,n+3,n+4,n+5. Sum of them is 6n+15, which is always odd
Sufficient

What statement 2 means is that,
if the numbers are 2,3,4,5,6,7 then n digit number formed by the series is 234567, which is divisible by 9.
From(2) : if the numbers chosen are 3,4,5,6 then 3456 is divisible by 9 and the sum is 18, which is even.
if the numbers chosen are 2,3,4,5,6,7 then 234567 is divisible by 9 and the sum is 27, which is odd.
Insufficient

Hence, the answer is A

Cheers!

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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 » Mon May 23, 2011 8:20 am

giovanni.gastone wrote:Source: Veritas

Is the sum of a series of n consecutive integers even?

(1) n=6
(2) The n digit number formed by the seriest is a multiple of nine

OA: A

Does anyone understand what the second statement is saying?

The wording of Statement 2 here is horrible, so I can understand why you'd find it confusing. Not only are they misusing the mathematical term 'series' (they mean to say 'sequence') but it also unclear what it means for a series to 'form' an 'n digit number'. How are we forming this number? I'm sure the interpretation Frankenstein gives above is what was intended by the question designer, but you'll never see such casual language in a real GMAT question.

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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giovanni.gastone: Senior | Next Rank: 100 Posts; Posts: 51; Joined: Fri Feb 18, 2011 5:35 pm; Location: Florence, Italy

by giovanni.gastone » Mon May 23, 2011 9:02 am

I agree. This question came from one of Veritas's CATs. So far, I have taken two and I have not only found spelling errors but also grammatical errors in some of their verbal questions. I was pretty surprised by the big difference in terms of quality between their books and their CAT questions. But, these CATs are good for practice anyway.

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