Question

(1 point) A pond contains 100 fish, of which 40 are carp. If 20 fish are caught from the lake, what are the mean and variance of the number of carp among those 20

Answer 1

Answer:

E(X) = 6

Var(X) = 3.394

Step-by-step explanation:

Let X represent the number of carp caught out of the 20 fishes caught. Now, if we are to assume that each

of the (100, 20) ways to catch the 20 fishes will be equally likely.

Thus, we can say that X fulfills a hypergeometric

distribution with parameters as follows;

n = 20, N = 100, k = 30

Formula for expected mean value in hypergeometric distribution is;

E(X) = nk/N

E(X) = (20 × 30)/100

E(X) = 6

Formula for variance is;

Var(X) = (nk/N) × [((n - 1)(k - 1)/(N-1))) + (1 - nk/N)]

Var(X) = ((20 × 30)/100) × [((20 - 1)(30 - 1)/(100 - 1)) + (1 - (20 × 30/100)]

Var(X) = 6 × 0.5657

Var(X) = 3.394