wastedyouth wrote:
PUNEETSCHDV wrote:
If n is an non-negative integer is 10^n+8 divisible by 18?
(1) n is a prime number
(2) n is even
IMO A
1) 10^n+8 will never divisible by 18 if n is prime no. define no means A is sufficient
2) n is even, if n=10, 10^n+8 is divisible by 18, but if n=2 it is not, two diff ans, means not sufficient
The above justification in red is wrong, right? The point is that in case 2 "n" could be zero, as zero is an even number. In this case, 10^0 = 1 and 1+8=9, which is not divisible by 18 (it gives 1/2). In every other case we get a "yes". So, this statement is not sufficient.
In case 1 it is always divisible by 18, because any positive power of 10 (except for 1 of course) would only add zeroes at the end of 10, and 8 would be added to that. Only by testing n=2, 100+8=108 and 108/18=6 we answer the question as "yes".
Then,
ANS is A.