I'm assuming that the distribution of X over 1,..., x are equally likely.

for x=1,2,3,4,5.

for y=1,...,x.

Hence for , where these are just integers.

X and Y are dependent since, for example, while

which is one way to prove dependency. If the rvs were independent, then the conditional probabilities would all be the same and they would be equal to the marginal distributions. But these two probabilities cannot both be equal to , since they are not equal to each other.