Consider three boxes, each containing 10 balls labelled $1,2,....,10$. Suppose one ball is randomly drawn from each of the boxes and is denoted by $n_i$, where $i$ represents the box, $(i = 1, 2, 3).$ Then, the number of ways in which the balls can be chosen such that $n_1<n_2<n_3$ is?
I tried doing this in different ways, but can't take the first step. I tried using multinomial theorem, but can't understand which terms to consider. Any help will be appreciated.