Divisble by 5

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dipzzz: Junior | Next Rank: 30 Posts; Posts: 24; Joined: Thu Mar 01, 2012 1:40 am; Thanked: 2 times

by dipzzz » Sun May 06, 2012 7:26 am

x is a positive number. If 9^x + 9^x+1 + 9^x+2 + 9^x+3 + 9^x+4 + 9^x+5 = y, is y divisible by 5?
1) 5 is a factor of x.
2) x is an integer.

isn't the question stem sufficient??

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Source: Beat The GMAT — Problem Solving | Sun May 06, 2012 7:26 am

Bill@VeritasPrep: GMAT Instructor; Posts: 1248; Joined: Thu Mar 29, 2012 2:57 pmFollowed by: 192 members; Location: Everywhere; Thanked: 503 times; GMAT Score:780

by Bill@VeritasPrep » Sun May 06, 2012 8:27 am

We need to know that x is an integer. If x is a decimal, then we could end up with decimal values for our terms, i.e. 9^2.2=~125.7

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klmehta03: Senior | Next Rank: 100 Posts; Posts: 74; Joined: Sun Sep 05, 2010 3:11 pm; Thanked: 3 times

by klmehta03 » Sun May 06, 2012 11:53 am

IMO A .
OA pls?

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dipzzz: Junior | Next Rank: 30 Posts; Posts: 24; Joined: Thu Mar 01, 2012 1:40 am; Thanked: 2 times

by dipzzz » Sun May 06, 2012 8:33 pm

OA D

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bryan88: Master | Next Rank: 500 Posts; Posts: 120; Joined: Mon Nov 07, 2011 10:54 pm; Location: Delhi; Thanked: 5 times

by bryan88 » Fri May 11, 2012 9:15 pm

Dont we get 9^(x) *66430 on expansion.

This is anyway divisible by 5.

Am i missing something?

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lathmanu: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Wed May 09, 2012 10:01 pm; Thanked: 2 times

by lathmanu » Sat May 12, 2012 12:48 am

bryan88 wrote:Dont we get 9^(x) *66430 on expansion.

This is anyway divisible by 5.

Am i missing something?

Yes the Question can be written as 66430*(9^x)

I would refer to Bill's reply.
We need to know that x is an integer.

Bill@VeritasPrep wrote:We need to know that x is an integer. If x is a decimal, then we could end up with decimal values for our terms, i.e. 9^2.2=~125.7

I first took B as the answer.
But after seeing the original answer as D, I realized that if 5 is a factor of x, then x is an integer.
A is also sufficient.

Thanks for the question dipzzz

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ihatemaths: Master | Next Rank: 500 Posts; Posts: 122; Joined: Tue May 01, 2012 6:05 am; Thanked: 3 times

by ihatemaths » Sat May 12, 2012 5:30 am

how do you people get 66430 ? did you compute fully ?

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