MHB Estimating the Probability of Earning a Certain Amount in a Weekend as a Waiter

AI Thread Summary
The waiter estimates his tips follow a left-skewed distribution with a mean of $8.20 and a standard deviation of $5.60, serving around 60 parties per weekend. The probability of earning at least $600 was calculated to be 0.0064. For the best 1% of weekends, the discussion focuses on finding the corresponding z-score using the z-scale. The user successfully identified that to find the z-score, they need to look for the value that corresponds to the 99th percentile. Understanding these calculations is essential for estimating potential earnings accurately.
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A waiter believes the distribution of his tips has a model that is slightly skewed to the left, with a mean of $\$8.20$ and a standard deviation of ​$\$5.60$. He usually waits on about 60 parties over a weekend of work. ​a) Estimate the probability that he will earn at least ​$\$600$. ​b) How much does he earn on the best 1​% of such​ weekends?

I worked out A and got 0.0064. I am having an issue on B. I don't understand how you obtain z​.
 
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I have figured out on my own. 1-00.1= .99 find it on the z-scale!
 
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