Question

The lengths, in inches, of adult corn snakes are normally distributed with a population standard deviation of 8 inches and an unknown population mean. A random sample of 25 snakes is taken and results in a sample mean of 58 inches. Identify the parameters needed to calculate a confidence interval at the 99% confidence level. Then find the confidence interval.

Answer 1

Parameters: z = 2.575

The 99% confidence interval for the lengths, in inches, of adult corn snakes are between 53.88 inches and 62.12 inches.

Explanation:

We have that to find our
`\alpha` level, that is the subtraction of 1 by the confidence interval divided by 2. So:

`\alpha = (1-0.99)/(2) = 0.005`

Now, we have to find z in the Ztable as such z has a pvalue of
`1-\alpha`.

So it is z with a pvalue of
`1-0.005 = 0.995`, so
`z = 2.575`

Now, find M as such

`M = z*(\sigma)/(√(n))`

In which
`\sigma` is the standard deviation of the population and n is the size of the sample.

`M = 2.575*(8)/(√(25)) = 4.12`

The lower end of the interval is the sample mean subtracted by M. So it is 58 - 4.12 = 53.88 inches

The upper end of the interval is the sample mean added to M. So it is 58 + 4.12 = 62.12 inches.

The 99% confidence interval for the lengths, in inches, of adult corn snakes are between 53.88 inches and 62.12 inches.