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integers

by ketkoag » Fri Jun 19, 2009 4:36 pm
If x and y are integers, is xy + 1 divisible by 3?
(1) When x is divided by 3, the remainder is 1.
(2) When y is divided by 9, the remainder is 8.

Please explain how OA is: C
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Source: — Data Sufficiency |
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by cramya » Fri Jun 19, 2009 7:16 pm
StmT I

x = 3k+1

y can be anything so dont have SUFF INFO to predict if xy+1 is divisible by 3

INSUFF


Stmt II

y = 9q+8

x can be anything so dont have SUFF INFO to predict if xy+1 is divisible by 3

INSUFF

Together:

xy + 1
(3k+1) (9q+8) + 1

27kq+24k+9q+8 +1

27kq+24k+9q+9

Since each of the terms is divisible by 3 their sum will be divisible by 3 with a remainder of 0

C
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