I would go with C)
Please post OA.
xy+1 divisibility by 3
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Source: Beat The GMAT — Data Sufficiency |
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sudhir3127
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jsl wrote:If x and y are integers, is xy+1 divisible by 3?
1) When x is divided by 3, the remainder is 1
1) When y is divided by 9, the remainder is 8
clearly 1 and 2 are insufficient..
therefore
X = 3a+1
Y= 9b+8
XY would be (3a+1)(9b+8)
u dont have to solve the equation ..its enuf if u realise that whole equation except the constant part will be will divisible by 3.
the constant part will be 8.
thus XY+ 1 will make the constant as 9 .hence divisble by 3.
hence C .
do let me know the OA
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jsl
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Thanks for the explanation. OA is C. Howevever, can I just question your comment here?sudhir3127 wrote:XY would be (3a+1)(9b+8)
u dont have to solve the equation ..its enuf if u realise that whole equation except the constant part will be will divisible by 3.
the constant part will be 8.
thus XY+ 1 will make the constant as 9 .hence divisble by 3.
I think that you do need to know the non-constant part of the equation because if this part is not a multiple of 3, then the whole numerator will not be a multiple of 3. The answer is correct because a is a multiple of 3 and b is a multiple of 9.
Is my logic correct here?
