Answer:
The sample size required is , in which M is the desired margin of error. If n is a decimal number, it is rounded up to the next integer.
Step-by-step explanation:
We have that to find our level, that is the subtraction of 1 by the confidence interval divided by 2. So:
Now, we have to find z in the Z-table as such z has a p-value of .
That is z with a pvalue of , so Z = 1.96.
Now, find the margin of error M as such
In which is the standard deviation of the population and n is the size of the sample.
Use 6.84 days as a planning value for the population standard deviation.
This means that .
What sample size would be required to obtain a margin of error of M days?
This is n for the given value of M. So
The sample size required is , in which M is the desired margin of error. If n is a decimal number, it is rounded up to the next integer.