1.Following is the probability distribution of a random variable that represents the number of extracurricular activities a college freshman participates in.

x	0	1	2	3	4
Px	0.05	0.13	0.45	0.21	0.16

(c) Find the probability that a student participates in at most three activities.

2.Compute the mean and standard deviation of the random variable with the given discrete probability distribution. round to three decimals

x	Px
6	0.17
2	0.07
2	0.24
4	0.28
6	0.24

3. Put some air in your tires: Let X represent the number of tires with low air pressure on a randomly chosen car. The probability distribution of

X is as follows.

x	0	1	2	3	4
Px	0.1	0.3	0.2	0.2	0.2

The probability that all four tires have low air pressure is

4. School days: The following table presents the numbers of students enrolled in grades 1 through 8 in public schools in a certain country.

Grade	Frequency (in 1000s)
1	3755
2	3634
3	3623
4	3589
5	3603
6	3663
7	3713
8	3762
Total	29,342

(c) Find the probability that the student is in third or fourth grade.