Question

Is the sample mean equal to the population mean?

Answer 1

No

Explanation:

The sample is a part of the population that is chosen to estimate the whole population but obviously it can't. It belongs at the forecast statistic. A value obtained from the population belong at descrittive statistic and regards the whole "population". When you calculate the average square deviation you use two different formulation.
for a sample `s=sqrt((sum(barX-Xi)^2)/(n-1))`.
for a population: `s=sqrt((sum(barX-Xi)^2)/(n))`
where `barX` is the average value, `Xi` is the single value, `n` is the number of the values mediated.