Hypergeometric distribution where we have a sample of k balls from an urn containing N, of which m are white and n are black.

```
expValErl(N = n + m, m, n = N - m, k)
varErl(N = n + m, m, n = N - m, k)
```

- N
Total number of balls (white and black) in the urn. \(N = n + m\)

- m
Number of white balls in the urn.

- n
Number of black balls in the urn. Can specify n instead of N.

- k
Number of balls drawn from the urn, k = 0, 1, ..., m + n.

Function :

`expValErl`

gives the expected value.`varErl`

gives the variance.

Invalid parameter values will return an error detailing which parameter is problematic.

The Hypergeometric distribution for \(N\) total items of which \(m\) are of one type and \(n\) of the other and from which \(k\) items are picked has probability mass function : $$Pr(X = x) = \frac{\left(\frac{m}{k}\right)\left(\frac{n}{k - x}\right)}{\left(\frac{N}{k}\right)}$$ for \(x = 0, 1, \dots, \min(k, m)\).

```
# With total balls specified
expValErl(N = 5, m = 2, k = 2)
#> [1] 0.8
# With number of each colour of balls specified
expValErl(m = 2, n = 3, k = 2)
#> [1] 0.8
# With total balls specified
varErl(N = 5, m = 2, k = 2)
#> [1] 0.36
# With number of each colour of balls specified
varErl(m = 2, n = 3, k = 2)
#> [1] 0.36
```