Hey guys I was reviewing old midsem exam papers and got stuck on this question I ll need any help you can give me.

Suppose we are taking samples from a population that has the same numbers of males and females but are concerned the sampling method may be biased. We take a sample of 20 people and test the null hypothesis H0: p = 0.5, where p is the mean proportion of females in a sample produced by the method.

The power of this test to detect a bias at the 5% level if the sampling method actually produces at least 80% females is......