During a night shift, 47 mints were selected at random from a production line and weighed. Their average weight was 21.48 g and standard deviation 0.91 g. (a) Estimate the true mean weight of mints manufactured in a night shift with 90% confidence. Interpret the interval. To create this interval, what assumption(s), if any, is(are) needed and how it(they) can be verified? (b) Estimate the variance of weight of mints manufactured in a night shift with 90% confidence.