1. For the data of Exercise 4.4, calculate the vari- ance using the formula
(a) of form (4.2.1);
(b) in Theorem 4.1.
2. The tar contents of 8 brands of cigarettes selected at random from the latest list released by the Federal Trade Commission are as follows: 7.3, 8.6, 10.4, 16.1, 12.2, 15.1, 14.5, and 9.3 milligrams. Calculate
(a) the mean;
(b) the variance.
3. 
The grade-point averages of 20 college seniors se- lected at random from a graduating class are as follows:
For the given phosphate data, ?nd
(a) the mean;
(b) the median;
(c) the mode.