Mean Maximization

JJ loves playing with averages. He has an array $A$ of length $N$. He wants to divide the array $A$ into two **non-empty** subsets $P$ and $Q$ such that the value of $mean(P) + mean(Q)$ is as large as possible. (Note that each $A_i$ must belong to either subset $P$ or subset $Q$). Help him find this maximum value of $mean(P) + mean(Q)$. As a reminder, the mean of a subset $X$ of size $M$ is defi