Answer:
The minimum sample size needed is
. If n is a decimal number, it is rounded up to the next integer.
is the standard deviation of the population.
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 = 1.645.
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.
How large a sample must she select if she desires to be 90% confident that her estimate is within 4 ounces of the true mean?
A sample of n is needed, and n is found when M = 4. So






The minimum sample size needed is
. If n is a decimal number, it is rounded up to the next integer.
is the standard deviation of the population.