Monte Carlo algorithm: Element in array
It doesn't matter what other elements are. We can assume that $k$ elements in $V$ are equal to $x$. Then the probability for a correct answer would be $k/n$ and $1-k/n$ for an incorrect answer. Then after $m$ tries, the probability of failure would be $(1-\frac{k}{n})^m$. 
And the probability of success in $m$ tries is the probability of not to be failed in every try, which is $1-(1-\frac{k}{n})^m$.