Answer:
The lower bound of the interval is 88.9mm and the upper bound is 93.1mm.
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 M as such
In which is the standard deviation of the population and n is the size of the sample.
The lower end of the interval is the sample mean subtracted by M. So it is 91 - 2.1 = 88.9mm.
The upper end of the interval is the sample mean added to M. So it is 91 + 2.1 = 93.1 mm
The lower bound of the interval is 88.9mm and the upper bound is 93.1mm.