Question

Some please explain how to do this? This is a sample question for my test, and I just don't understand!

When parking a car in a downtown parking lot, drivers pay according to the number of hours or fraction thereof. The probability distribution of the number of hours X cars are parked has been estimated as follows:

X=x	P(x)
1	0.225
2	0.104
3	0.106
4	0.081
5	0.067
6	0.028
7	0.022
9	0.367

Find the mean and standard deviation of the number of hours the cars parked.

Answer 1