In a random sample of 500 items from a large lot of manufactured items, there were 40

Question:

In a random sample of 500 items from a large lot of manufactured items, there were 40 defectives.
(a) Find a 90% confidence interval for the true proportion of defectives in the lot.
(b) Is the assumption of normal approximation valid?
(c) Suppose we suspect that another lot has the same proportion of defectives as in the first lot. What should be the sample size if we want to estimate the true proportion within 0.01 with 90% confidence?