This question might have been asked before, but I am not able to find it in a search.
If n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24, what is the value of r?
1) n is not divisible by 2
2) n is not divisible by 3
seems C since n is a prime integer greater tham 3, r when (n-1)(n+1) is divided by 24 is 0.