Advanced Quant (5 ed.) page 83, Quesiton 4

[Indogermanican]

Question:

If n is a positive integer, is n-1 divisible by 3 ?

(1) n^2+n is not divisible by 6.

(2) 3n=3k+3, where k is a positive multiple of 3.


The OA suggests that statement 2 is insufficient but I've tried a different way to solve this and came to the conclusion that (2) is sufficient.

My solution for statement 2
3n = 3k+3
3n-3 = 3k
3(n-1) = 3k
n-1 = k
And with k being a positive multiple of 3, n-1 should be divisible by 3, making statement 2 sufficient.

Can someone explain where I went wrong?

Thanks,
alex

[tim]

you copied the problem wrong.. :)