How to prove the following formula?
$$\sum_{j=0}^{n-1} \sum_{k=0}^{j} \frac{{n}\choose{k}}{{n-1}\choose{j}} = 2^{n-1}\sum_{j=0}^{n-1} \frac{1}{{n-1}\choose{j}}$$
I tried induction and manipulating the binomial coefficients but couldn't prove it. I also tried to write the term $2^{n-1}$ as $\sum_{k=0}^{n-1} {{n-1}\choose{k}}$. That's a nice structure at least: sum of the binomial coefficients times the sum of their reciprocals. But how do we "cut" the inner sum at $j$ and turn $n-1$ in the numerator into $n$?