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...

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 E(Z) and Var(Z).

(2) What is the probability that the daily total turnover Z is greater than
190,000?