Use the following expression for the number of elements of a sample, related to a certain proportion a Z-score:
[tex]n=(\frac{Z}{E})^2\cdot p\cdot q[/tex]where,
p: percentage of applicants in decimal form = 0.22 (28%)
q = 1 - p = 1 - 0.22 = 0.78
E: percentage margin = 0.05 (5%)
Z-score for 99% confidence = 2.576 (found in a Z-score table)
Replace the previous values of the parameters into the formula for n and simplify:
[tex]n=(\frac{2.576}{0.06})^2\cdot0.22\cdot0.78\approx316[/tex]Hence, approximately 316 students are needed for the sample.
