N is the sum of two positive integers p and q. Is N divisible by 8?
N = p+q
Is N = 8x? where x, any positive integer
1) Neither p nor q is divisible by 8.
Case (1) Either p, q can both be odd, resulting in an even number which is only divisible by 2
Case(2) p,q one of them resulting in odd values, which is not a multiple of 8
Case (3) p,q one of them even and other is odd multiple of 4, resulting in a number not divisible by 8 (4+8 = 12)
Case(4) p,q can be both even or odd multiples of 4 resulting in number divisible by 8
(4+12 = 16) ---- both odd multiples of 4
16 + 8 = 24 ----- both even multiples of 4
But we don't know anything about p,q except they are not divisible by 8
Insufficient
2) Both p and q are individually divisible by 4.
Case (1) p,q one of them even and other is odd multiple of 4, resulting in a number not divisible by 4 (4+8 = 12)
Case(2) p,q can be both even or odd multiples of 4 resulting in number divisible by 8
(4+12 = 16) ---- both odd multiples of 4
16 + 8 = 48 ----- both even multiples of 4
But we don't know anything about p,q except they are individually divisible by 4
Insufficient
(1) and (2) together, sufficient
As p,q are not multiples of 8, and multiples of 4 which implies they are odd multiples of 4
4+12 = 16
Clearly we can say, resultant is divisible by 8
sufficient
Option C is correct