Given $n$ distinct coupons, each package contains exactly one of the $n$ coupons with the probability $\dfrac{1}{n}$. I'm interested in the expected number of packages one has to buy so that one has each coupon at least two times.
My approach was to to just imagine that there are $2n$ coupons to choose from and we're interested in computing the expected number of coupons we have to buy to get all of them ($2n$). I'm however very uncertain whether this approach is correct.