Compute the sample mean and variance from data

Question

Discuss the below:

Calculating Mean and Variance.

A. Following sample data shows the weekly closing price of ABC stock.  Compute the sample mean and variance from this data set.

Closing price
89
98
78
86
79
98
88
86
89
98

B. Following sample data arranged in a frequency distribution table.  Use Excel to compute the sample mean and variance from this data set.

Reading scores	Frequency
81	7
82	8
83	5
84	9
85	4
86	7
87	8
88	5
90	9
91	8

C. Following probability distribution table shows the reading scores, x, of 4^th graders from a given school district.  Use Excel to calculate the mean and variance from this data set.

x	P(x)
81	0
82	0.01
83	0.04
84	0.12
85	0.21
86	0.24
87	0.21
88	0.12
90	0.04
91	0.01