Central Limit Theorum

Calculator: https://www.easycalculation.com/statistics/central-limit-theorem.php

If you have n - then you can get the SAMPLE Mean and SAMPLE Standard Deviation

to plug into your Z scores.

See Also Dan Lemay's WHAT IS THE PROBABILITY https://sites.google.com/site/jilmacmath/statistics/sampeling

or

Confidance Intervals. THE RANGE https://sites.google.com/site/jilmacmath/statistics/confidence-intervals

Both of these follow questions that revolve around the Central Limit Theorum