4.25 One of the leading retail banks in China is the Postal Savings Bank of China, located in Beijing. Suppose the number of arrivals per minute at the bank, which has around 40,000 outlets, was recorded over a period of 200 minutes with the results shown in the table below.

Arrivals 0 1 2 3 4 5 6 7 8 Frequency 22 41 44 37 26 16 8 4 2 Find the mean and standard deviation of the number of arrivals at the bank.