confidence intervals

[Scoobiegal]

Can someone please show me how to do this problem? Any help will be greatly appreciated.

Out of a sample of 459 randomly selected light bulbs tested in a laboratory, 291 lasted more than 500 hours.

a. Find a 90% confidence interval for the true population proportion of light bulbs that will last more than 500 hours.

b. Find a 95% confidence interval for the true population proportion of light bulbs that will last more than 500 hours.

[quark]

First you find the sample porportion: phat=291/459=0.634

Then the standard error of the proportion: SE=sqrt[0.634*(1-0.634)/459]

The 90% confidence interval is: phat +- 1.64*SE

The 95% confidence interval is: phat +- 1.96*SE