A waiterbelieves the distribution of his tips has a model that is slightly skewed to the left​, with a mean of ​$8.60 and a standard deviation of $4.20. He usually waits on about 50 parties over a...

A waiterbelieves the distribution of his tips has a model that is slightly skewed to the left​, with a mean of ​$8.60 and a standard deviation of $4.20. He usually waits on about 50 parties over a weekend of work.

​a) Estimate the probability that he will earn at least ​$450.

​b) How much does he earn on the best 5​% of such​ weekends?