probability?

Question

For a population with a standard deviation of 20: If you wanted your sample mean to be within 1 point of the populations mean (on the average), how large a sample would you use?

Answer 1

If the standard deviation of the population is std. If you pick a sample on the standard deviation of the sample is
std/n^1/2

So you have 1 =20/n^1/2

n^1/2= 20 and

n=400

Answer 2

At least 441.