Answer:
A sample size of at least 271 is required.
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 .
So it is z with a pvalue of , so
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.
Maxium error of 0.12.
How large of a sample is required to estimate the mean usage of electricity?
We need a sample size of at least n.
n is found when
So
Rounding up
A sample size of at least 271 is required.