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If x is a positive integer, is the remainder 0 when

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Manager
Joined: 25 May 2007
Posts: 231
Schools: Cornell
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If x is a positive integer, is the remainder 0 when [#permalink]  24 Nov 2007, 07:47
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If x is a positive integer, is the remainder 0 when (3^x+1)/10?

(1) x=3n+2, where n is a positive integer
(2) x>4

I found funny OA.
SVP
Joined: 29 Aug 2007
Posts: 2496
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Kudos [?]: 562 [0], given: 19

Re: DS - remainder [#permalink]  24 Nov 2007, 13:03
solidcolor wrote:
If x is a positive integer, is the remainder 0 when (3^x+1)/10?

(1) x=3n+2, where n is a positive integer
(2) x>4

I found funny OA.

which one is correct: "[(3^x) + 1] / 10" or 3^(x+1) / 10 ?
CEO
Joined: 17 Nov 2007
Posts: 3577
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
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Kudos [?]: 2168 [0], given: 359

Expert's post
E.

(3^x+1)/10 means that last unit of (3^x) is 9

for 3^x
x=0: 1
x=1: 3
x=2: 9
x=3: 7
x=4: 1

so x=4k-2 (k positive integer)

1.x=3n+2 insuff

2.x>4 insuff

1&2. insuf
Senior Manager
Joined: 22 Sep 2005
Posts: 279
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Kudos [?]: 90 [0], given: 1

walker wrote:
E.

(3^x+1)/10 means that last unit of (3^x) is 9

for 3^x
x=0: 1
x=1: 3
x=2: 9
x=3: 7
x=4: 1

so x=4k-2 (k positive integer)

1.x=3n+2 insuff

2.x>4 insuff

1&2. insuf

E too.

3^(x+1)/ 10 if ends in 0

1) x=3n+2

then 3^(3n+2+1)=3^(3n+3)=3^3(n+1). NOT SUF

2) x>4. NOT SUF
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