Is n-1 divisible by 3?

[bizwizashish]

Great eye opener... because in such questions top of mind says that since consecutive .. hence divisible by 3.. hence A..

The only prob is .. i ahve seen so many questions on this type on this forum and some other places as well.. that it never occurred in my mind..

certainly useful..

Thanks

[KrazyGMAT]

if u choose n=-1 then
its -1(-1+1)=0 not -1...which is divisible by 3....so u cant pick -1 for statement 1.so answer in OA is wrong

[tinbilly]

In my opinion, there's a flaw in the Official Explanation. We all know that 0 is divisible by any number, except 0. My answer is A. Here is why.

(1) n² + n = n(n+1) is not divisible by 3
==> n = 3m + 1 & n+1 = 3m + 2, where m is an integer.
==> n-1 = 3m is divisible by 3
==> Sufficient

(2) 3n+5 >= k + 8, where k is a positive multiple of 3
==> n >= k/3 + 1
Given that k is a positive multiple of 3, we know that n must be greater than or equal to 2. We get no further information about n.
==> Insufficient

From (1) & (2), answer is A.