1. If I want to find out what % of the local population (say, 10 million total people) consider themselves to be music lovers, how many people do I need to poll before I can achieve, say 95% confidence level with, say a confidence interval of +-2.5% (for example 30-35%)? Or +-5% (for example 30-40%)?

2. Similarly, if I want to ask X number of people in the local population what THEY think the true % of the local population is who consider themselves to be music lovers, how many people would I need to ask before I can achieve 95% confidence level that the mean answer I get from that X number of people is +-2.5 or +-5% of the true mean (the mean that I would have had I asked every single person in the local population)?

Anything would be appreciated.