[2008] Topic 3: Review of Statistics I: Probability and Probability Distribut

aianjie

 

AIM 1: Define random variables, and distinguish between continuous and discrete random variables.

1、Which of the following statements about probability is most accurate?

A) A conditional probability is the probability that two or more events will happen concurrently.

B) An outcome is the calculated probability of an event.

C) Out of a sample of 100 widgets 10 were found to be defective, 20 were perfect, and 70 were OK. The probability of picking a perfect widget at random is 29%.

D) An event is a set of one or more possible values of a random variable.

aianjie

 

The correct answer is D

Conditional probability is the probability of one event happening given that another event has happened. An outcome is the numerical result associated with a random variable. The probability of picking a perfect widget is 20 / 100 = 0.20 or 20%.

aianjie

 

2、Let A and B be two mutually exclusive events with P(A) = 0.40 and P(B) = 0.20. Therefore:fficeffice" />

A) P(B|A) = 0.20.

B) P(A or B) = 0.52.

C) P(A and B) = 0.

D) P(A and B) = 0.08.

aianjie

 

The correct answer is C

If the two evens are mutually exclusive, the probability of both ocurring is zero.

aianjie

 

AIM 2: Define the probability of event.

1、The following table summarizes the availability of trucks with air bags and bucket seats at a dealership.

	Bucket seats	No Bucket Seats	Total
Air Bags	75	50	125
No Air Bags	35	60	95
Total	110	110	220

What is the probability of randomly selecting a truck with air bags and bucket seats?

A) 0.34.

B) 0.16.

C) 0.28.

D) 0.57.

aianjie

 

The correct answer is A

75 / 220 = 0.34.

aianjie

 

2、If two fair coins are flipped and two fair six-sided dice are rolled, all at the same time, what is the probability of ending up with two heads (on the coins) and two sixes (on the dice)?

A) 0.4167.

B) 0.0069.

C) 0.0039.

D) 0.8333.

aianjie

 

The correct answer is B

For the four independent events defined here, the probability of the specified outcome is 0.5000 × 0.5000 × 0.1667 × 0.1667 = 0.0069.

aianjie

 

3、A dealer in a casino has rolled a five on a single die three times in a row. What is the probability of her rolling another five on the next roll, assuming it is a fair die?

A) 0.001.

B) 0.167.

C) 0.500.

D) 0.200.

aianjie

 

The correct answer is B

The probability of a value being rolled is 1/6 regardless of the previous value rolled.