Answer:
The minimum sample size needed is 39.
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 Ztable as such z has a pvalue of .
That is z with a pvalue of , so Z = 2.575.
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.
Assuming that the standard deviation of the number of hours is 120 hour
This means that
The minimum sample size needed in order to construct a 99% confidence interval for the mean number of hours of flight time of all such pilots, to within 50 hours, is about?
The minimum sample size needed is n.
n is found when
So
Rounding up
The minimum sample size needed is 39.