Question

Dairy cows at large commercial farms often receive injections of bST (Bovine Somatotropin), a hormone used to spur milk production. Bauman et al. (Journal of Dairy Science, 1989) reported that 12 cows given bST produced an average of 28.0 kg/d of milk. Assume that the standart deviation of milk production is 2.25 kg/d. (a) Find a 99% confidence interval for the true mean milk production. Round your answers to two decimal places (e.g. 98.76).

Answer 1

Answer:

The 99% confidence interval for the true mean milk production is between 26.33 kg/d and 29.67 kg/d.

Step-by-step explanation:

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

$\alpha = \frac{1 - 0.99}{2} = 0.005$

Now, we have to find z in the Z-table as such z has a p-value of $1 - \alpha$.

That is z with a pvalue of $1 - 0.005 = 0.995$, so Z = 2.575.

Now, find the margin of error M as such

$M = z\frac{\sigma}{\sqrt{n}}$

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

$M = 2.575\frac{2.25}{\sqrt{12}} = 1.67$

The lower end of the interval is the sample mean subtracted by M. So it is 28 - 1.67 = 26.33 kg/d.

The upper end of the interval is the sample mean added to M. So it is 28 + 1.67 = 29.67 kg/d.

The 99% confidence interval for the true mean milk production is between 26.33 kg/d and 29.67 kg/d.