The number of arrivals per minute at the bank located in a central business district of large city was recorded over a period of 200 minutes, with the results which are given below:
Arrivals Frequency
-0 14
1 31
2 47
3 41
4 29
5 21
6 10
7 5
8 2
A) find out the expected number of arrivals per minute.
B) find out the standard deviation.