Answer:
The sample required is 
Step-by-step explanation:
From the question we are told that
The standard deviation is 
The margin of error is 
Given that the confidence level is 99% then the level of significance is mathematically evaluated as



Next we will obtain the critical value
from the normal distribution table(reference math dot armstrong dot edu) , the value is

The sample size is mathematically represented as
![n = [ \frac{Z_{\frac{\alpha }{2} } * \sigma }{E} ]^2](https://tex.z-dn.net/?f=n%20%3D%20%5B%20%5Cfrac%7BZ_%7B%5Cfrac%7B%5Calpha%20%7D%7B2%7D%20%7D%20%2A%20%20%5Csigma%20%7D%7BE%7D%20%5D%5E2)
substituting values
![n = [ \frac{ 2.58 * 9 }{2} ]^2](https://tex.z-dn.net/?f=n%20%3D%20%5B%20%5Cfrac%7B%202.58%20%2A%20%209%20%7D%7B2%7D%20%5D%5E2)

Answer:
D
Step-by-step explanation:
Answer:
To obtain a valid approximation for probabilities about the average daily downtime, either the underlying distribution(of the downtime per day for a computing facility) must be normal, or the sample size must be of 30 or more.
Step-by-step explanation:
Central Limit Theorem
The Central Limit Theorem establishes that, for a normally distributed random variable X, with mean
and standard deviation
, the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean
and standard deviation
.
For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.
For a proportion p in a sample of size n, the sampling distribution of the sample proportion will be approximately normal with mean
and standard deviation 
In this question:
To obtain a valid approximation for probabilities about the average daily downtime, either the underlying distribution(of the downtime per day for a computing facility) must be normal, or the sample size must be of 30 or more.