Confidence intervals and point estimate problems

[colle]

I am lost on how to do these two problems and can't find info on how to solve them anywhere. If anyone can get me on the right track as to how to start, that would be amazing!

1. A 99% confidence interval for a population mean was reported to be 152 to 158. If the standard deviation is 10, what sample size was used in this study?

2. A survey for a sample of 300 students resulted in 175 yes responses, 110 no responses, and 15 no opinions. What is the point estimate of the proportion in the population who respond "no opinion"?

 

[chisigma]

I am lost on how to do these two problems and can't find info on how to solve them anywhere. If anyone can get me on the right track as to how to start, that would be amazing!

1. A 99% confidence interval for a population mean was reported to be 152 to 158. If the standard deviation is 10, what sample size was used in this study?

As reported in...

http://mathhelpboards.com/questions-other-sites-52/unsolved-statistics-questions-other-sites-part-ii-1566-post12072.html#post12072

... is [approximately] $ \text{erfc}\ (x) = .01$ for $x \sim 1.8$ so that is $\displaystyle \frac{10}{\sqrt{n}} = \frac{5}{3} \implies n=36$... Kind regards $\chi$ $\sigma$