Hi ,
I have some issues with the following problems:

Problem 1:
In a product reliability study, let p denote the probability that the product will last five years or more after normal usage. The study used a random sample of n=150 test products and found that 80% lasted five years or more.
a- Give the best point estimate of p
b- Find the 95% confindence interval for p.
c- Is p in your confidence interval?

In class we were given a table of formula to find the confidence interval. (I think you now what I am talking about) How to choose the good formula?

Problem 2:
Suppose a randon variable, X is normally distributed with mu(mean)=30 and sd(standard deviation) =5. What sample size is necessay to ensure that the 94% confidence interval for mu has:
a- a width of at most 2?
b- a width of at most 4?

thank you