What's the difference between population variance and sample variance.

i would like to apply those techniques to cross this challenge below:

1. The Centre for Disease Control (CDC) states that the variation in the particles allowed in by a N95 mask should not exceed a specific value. LASCO Mask is concerned that the variability in the particles allowed in through their N95 masks may be above the specified value. To examine this, they evaluated a random sample of 50 masks. a) What is the probability that the sample variance of the emissions on production days is more than three times the population variance? b) What assumption do you have to make to calculate your answer in part (a)