probability

1.

If 25 tickets are sold and 2 prizes are to be awarded, find the probability that one person will win both prizes if that person buys exactly 2 tickets.

2.

According to an Internet posting, 80% of adults enjoy drinking beer. A group of 7 adults is chosen randomly. The probability that no more than 3 of them enjoy drinking beer is:

3.

If a gambler rolls two dice and gets a sum of 10, he wins $10, and if he gets a sum of three, he wins $20. The cost to play the game is $5. What is the expectation of this game?

4.

Given that Z is a standard normal random variable, P(-1.0 < Z < 1.5) is

5.

Given that Z is a standard normal variable, the value z for which P(Z < z) = 0.2580 is

6. The average height of flowering cherry trees in a nursery is 11 feet. If the heights are normally distributed with a standard deviation of 1.6, find the probability that a randomly selected cherry tree in this nursery is less than 13 feet tall.

7. Suppose that the average weekly earnings for employees in general automotive repair shops is $450, and that the standard deviation for the weekly earnings for such employees is $50. A sample of 100 such employees is selected at random. Find the probability that the mean of the sample is greater than $460.

8. A set of final exam scores in an organic chemistry course was found to be normally distributed, with a mean of 73 and a standard deviation of 8. What is the probability of getting a score higher than 71 on this exam?