Normal approximation to the hypergeometric distribution. Let $n, m, k$ be positive integers and suppose that they tend to infinity in such a way that
$$
\frac{r}{n+m} \rightarrow t, \quad \frac{n}{n+m} \rightarrow p, \quad \frac{m}{n+m} \rightarrow q, \quad h\{k-r p\} \rightarrow x
$$
where $h=1 / \sqrt{(n+m) p q t(1-t)}$. Prove that
$$
\binom{n}{k}\binom{m}{r-k} /\binom{n+m}{r} \sim h \mathrm{n}(x) .
$$
Hint: Use the normal approximation to the binomial distribution rather than Stirling's formula.