Question:
A supermarket employes 24 shop-assistants. 20 of them achieve an average daily turnover of $8000, whereas 4 achieve an average daily turnover of $ 10,000. The corresponding standard deviations are $2400 and $3000, respectively. The daily turnovers of all shop-assistants are independent and have a normal distribution. Let Z be the daily total turnover of all shop-assistants.
(1) Determine and . E(Z) Var(Z)
(2) What is the probability that the daily total turnover Z is greater than $ 190,000?