1.-Statistical exam scores are normally distributed with

mean of 85 and standard deviation 7 . What fraction of the ratings is found

between 60 and 70?

2.-In a community of 300 people, 110 have children, 120 are employed. If there are 80

people who do not have children and who do not have a job:

1) Prepare the contingency table

b) If a bachelor is selected at random. What is the probability that you are an entrepreneur?

3.-Assume that male and female births are equally likely and that

the birth of any baby does not affect the likelihood of the gender of any other

baby. Calculate the probability that exactly 5 girls will be born in 15 births.

4.-Let X be the survival time, in days, of guinea pigs exposed to a

gamma radiation of 300 rads (absorbed radiation dose). X is supposed to follow

a gamma distribution with parameters a = 9 and = 18

a)

Calculate the mean and variance of survival.

b)

Calculate the probability that a rabbit will survive between 80 and 120 days.

5.-The time in years it takes for a radioactive substance to degrade is distributed

exponentially with the density function