Discrete and Continuous Random Variables

The weight of written reports produced in a certain department has a Normal distribution with mean 60 g and standard deviation 12 g. The probability that the next report will weigh less than 45 g is

• .1056
• .3944
• .1042
• .8944

Is this a probability distribution?

• No
• Yes

Is this a probability distribution?

• No
• Yes

The probability of each value of the random variable must be between or equal to ________?

• 0
• 1
• 0 and 1
• none of the above

What is the difference between a discrete random variable and a continuous random variable?

• A discrete random variable takes all values in an interval of numbers while a continuous random variable has a fixed set of possible values with gaps between.
• A discrete random variable has a fixed set of possible values with gaps between while a continuous random variable takes all values in an interval of numbers.
• A discrete random variable takes only negative numbers while a continuous random variable takes both positive and negative numbers.
• A discrete random variable takes both positive and negative numbers while a continuous random takes only negative numbers.

If Gonzalo's score is 87%, the class average is 82%, and the SD is 4, what is Gonzalo's Z-score?

• -1.25

• +1.25

• +1.20

• +1.02

A marketing survey compiled data on the number of cars in households.  If X = the number of cars, and we omit the rare cases of more than 5 cars, then X has the following probability distribution: 
X         0         1         2       3         4        5 
P(X)  0.24  0.37  0.20  0.11  0.05  0.03
What is the probability that a randomly chosen household has at least two cars?

• 0.20
• 0.29
• 0.39
• 0.61

The table represents the probability of guessing correct on a 5 question true-false quiz.  Find the probability for at least 4 questions correct.

• .03125
• .15625
• .3125
• .1875

A tennis player makes a successful first serve 60% of the time.  If she serves 20 serves, what is the mean number of good first serves?  Assume that each serve is independent.

• 12
• 18
• 8
• 15

A stockbroker estimates that at the end of the year, there is a 40% chance a stock will be worth $50, a 35% chance it will be worth $60 and a 25% chance it will be worth $70.
What expected value does this broker assign to this stock's end-of-the-year price?

• $58.50
• $60.00
• $62.50
• $65.00