Dividend and divisor problem?

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prees20: Junior | Next Rank: 30 Posts; Posts: 12; Joined: Fri Mar 28, 2008 10:07 am

by prees20 » Fri Aug 01, 2008 12:11 am

If x is an integer and y = 3x + 2, which of the following CANNOT be a divisor of y ?
(A) 4
(B) 5
(C) 6
(D) 7
(E) 8

I dont understand how C is the answer?
-----
Ans - C

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Source: Beat The GMAT — Problem Solving | Fri Aug 01, 2008 12:11 am

pepeprepa: Legendary Member; Posts: 661; Joined: Tue Jul 08, 2008 12:58 pm; Location: France; Thanked: 48 times

by pepeprepa » Fri Aug 01, 2008 12:23 am

C is the answer because other answers can be a divisor of y. If you can divide y by all the proposals except one, so this one is the answer: they ask you "which one CANNOT be a divisor of y".

A) 3*2+2=8 divisible by 4
B) 3*6+2=20 divisible by 5
D) 3*4+2=14 divisible by 7
E) 3*2+2=8 divisible by 8

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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

Re: Dividend and divisor problem?

by Ian Stewart » Fri Aug 01, 2008 3:33 am

prees20 wrote:If x is an integer and y = 3x + 2, which of the following CANNOT be a divisor of y ?
(A) 4
(B) 5
(C) 6
(D) 7
(E) 8

I dont understand how C is the answer?
-----
Ans - C

Or you can look at it this way:

If y = 3x + 2, then y is two larger than a multiple of 3. That is, the remainder is 2 when you divide y by 3. So y is not divisible by 3.

If y isn't divisible by 3, y definitely is not divisible by 6.

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

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malolakrupa: Senior | Next Rank: 100 Posts; Posts: 58; Joined: Fri Jul 18, 2008 12:26 pm; Thanked: 2 times

by malolakrupa » Fri Aug 01, 2008 11:34 am

For a number to be divisible by 6 it needs to be a divisible by 2 and 3 both . 3 times any number + 2 could be divisible by 2 and not by 3 . Hence 6 is the only divisor in the list.

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