Question

Coliform bacteria are randomly distributed in a river at an average concentration of 1 per 20cc of water. What is the variance of the number of Coliform bacteria in a sample of 40cc of water

Answer 1

`Var = 1.9`

Explanation:

Given

`p = (1)/(20)` i.e. 1 per 20cc of water

`n = 40` -- sample size

Required

The variance

This is calculated using:

`Var = np(1 - p)`

So, we have:

`Var = 40 * (1)/(20) * (1 - (1)/(20))`

`Var = 40 * (1)/(20) * (19)/(20)`

`Var = 2 * (19)/(20)`

`Var = (38)/(20)`

`Var = 1.9`