Question

which mean should i use to calculate the interval for confidence level?

Answer 1

A confidence level is a level of confidence in a particular thing. You can't just say "the confidence level" without saying what it's confidence OF.

Use the mean of your sample (480) if you are talking about how confident you are in the sample mean.

So in other words, to answer what question?

Answer 2

You always use the sample value in creating a confidence interval, never the population value.

Answer 3

When constructing the distribution for the hypothesis test, you'll use:

Normal(population mean, population variance ÷ sample size)

So you need the population mean, which is 500.