How Large Should n Be for a Specific Confidence Interval Width?

[Artusartos]

You have a random sample of size n from a normal distribution with unknown mean μ and variance 100. You want to find n large enough so that the length of the confidence interval (from left endpoint to right endpoint) is at most .2. Find such a value of n so that n is as small as possible. If you instead were willing to have a confidence interval with twice this length, what would you need to do to n? (Note: All confidence intervals in this problem are 95 percent confidence intervals.)

I attached my answer...

 

[pasmith]

Looks right.

 

[Artusartos]

Looks right.

Thanks :)