A restaurant server believes the distribution of their tips has a model that is slightly skewed to the
right​, with a mean of ​$ 9.40 and a standard deviation of ​$ 5.20. They usually wait on about
50 parties over a weekend of work.

​a) Estimate the probability that they will earn at least ​$ 500 in tips.

​b) How much do they earn on the best 10​% of such​ weekends?