This video covers problems where you are given a proportion or percentage of a sample which has come quality (p), and you are asked to estimate a confidence interval for the population proportion with that same characteristic. Since you're working with p and q, as usual this only works for larger sample sizes.
Minimum Sample Size for Proportion Estimates
As you know, bigger samples lead to smaller margins of error. This video covers the type of problem where they give you the margin of error, then ask you to calculate the minimum sample size you'd have to take in order to accomplish that margin of error.
If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)