value of n

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gmataug08: Master | Next Rank: 500 Posts; Posts: 105; Joined: Sat May 17, 2008 8:12 pm; Thanked: 6 times

by gmataug08 » Sat Dec 06, 2008 3:28 pm

Question : For what natural number 'n' is the fraction (3n-4)/5 is an integer?

Options :
A : For n + 3 divisible by 5
B : For n + 1 divisible by 3
C : For even natural ‘n’
D : For 2n + 3 divisible by
E : For n - 3 divisible by 5

OA: A

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Source: Beat The GMAT — Problem Solving | Sat Dec 06, 2008 3:28 pm

cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Sat Dec 06, 2008 3:43 pm

Please complete choice D)

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niraj_a: Legendary Member; Posts: 708; Joined: Sun Jun 01, 2008 4:59 amFollowed by: 1 member; Location: USA; Thanked: 13 times

by niraj_a » Sat Dec 06, 2008 4:12 pm

i chose E

if N = 8 then n-3 will be divisible by 5, and so will the term in the original stem

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gmataug08: Master | Next Rank: 500 Posts; Posts: 105; Joined: Sat May 17, 2008 8:12 pm; Thanked: 6 times

by gmataug08 » Sat Dec 06, 2008 4:13 pm

option D was incomplete .

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gmataug08: Master | Next Rank: 500 Posts; Posts: 105; Joined: Sat May 17, 2008 8:12 pm; Thanked: 6 times

by gmataug08 » Sat Dec 06, 2008 4:15 pm

niraj_a wrote:i chose E

if N = 8 then n-3 will be divisible by 5, and so will the term in the original stem

that was my answer too. But OA was different, so posted here , incase I missed something (other than the rest of option D)

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Sat Dec 06, 2008 4:17 pm

So we have 4 choices. ok..

I did it by process of elimination

3n-4/5 = k where k is some integer

3n-4 = 5k

3n-4=0
3n-4=5
3n-4=10(n=2)
3n-4=15
3n-4=20
3n-4=25 (n=7)

The only choices that fits 2 and 7 so far is A)

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gmataug08: Master | Next Rank: 500 Posts; Posts: 105; Joined: Sat May 17, 2008 8:12 pm; Thanked: 6 times

by gmataug08 » Sat Dec 06, 2008 4:28 pm

if I have n= 8 , E satisfies the condition.

I guess, we have more than one answer. :roll:

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Sat Dec 06, 2008 4:32 pm

If I have n= 8 , E satisfies the condition.

U r correct. This makes A) fail.

Whats confusing about this question is it akss for one value of n so yes there could be multiple answer choices that satisfy.

Whats the source?

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Zipper: Master | Next Rank: 500 Posts; Posts: 119; Joined: Sun Nov 30, 2008 2:47 am; Thanked: 11 times

by Zipper » Sat Dec 06, 2008 5:02 pm

(3n-4)/5=integer

so (3n-4)=units digit 9 or 4

n=3, 8, 13, 18, 23, 28 and so on.

Clearly visible only E fits.

It's not more than one answer since A doesn't even fit. It's clear that this question is very messed up since even the answers are not complete(D).

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