AP Statistics : AP Statistics

Study concepts, example questions & explanations for AP Statistics

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Example Questions

Example Question #3 : Random Variables

Which of the following would be considered a binomial experiment?

Possible Answers:

Rolling six dice until three of the dice show the number two

Given that 36% of the population has blond hair, predicting the probability that the majority of students at a public university have blond hair

Selecting four cards from a deck in an attempt to get all of the same face (e.g., all aces)

Rolling 25 dice to find the distribution of the number of spots on the faces

Predicting the probability that in a series of ten games of Rock, Paper, Scissors played with random strategy, one individual obtains six victories

Correct answer:

Predicting the probability that in a series of ten games of Rock, Paper, Scissors played with random strategy, one individual obtains six victories

Explanation:

There are four conditions that need to be satisfied for a binomial experiment:

1) Each trial must have two outcomes.

2) Each trial must be independent.

3) All trials must be identical.

4) The probabilities of the outcomes remain constant must not change with each trial.

The only choice that satisfies all four of these conditions (and is therefore a binomial experiment) is the rock-paper-scissors scenario.

Example Question #1 : Random Variables

Which of the following is a discrete random variable?

Possible Answers:

The length of a random caterpillar

The rate of return on a random stock investment

The amount of water that passes through a dam in a random hour

The number of times heads comes up on 10 coin flips

Correct answer:

The number of times heads comes up on 10 coin flips

Explanation:

A discrete variable is a variable which can only take a countable number of values. For example, the number of times that a coin can come up heads in ten flips can only be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. Thus, there are a countable number of possible outcomes (in this case 11). This is true for coin flips, but not for caterpillar length, water flow, or rates of return for stocks.

Example Question #4 : Random Variables

Let us suppose you are a waiter. You work your first four shifts and receive the following in tips: (1) 20, (2) 30, (3) 15, (4) 5. What is the mean amount of tips you will receive in a given day?

Possible Answers:

Correct answer:

Explanation:

The answer is 17.5. Simply take the values for each day, add them, and divide by the total number of days to obtain the mean: 

Example Question #3 : Random Variables

There are  collectable coins in a bag.  are  ounces,  are  ounces,  are  ounces, and  are  ounces. If one coin is randomly selected, what is the mean possible weight in ounces?

Possible Answers:

Correct answer:

Explanation:

We are required to find the mean outcome where the probability of each possible result varies--the random/weighted mean. 

First, multiply each possible outcome by the probability of that outcome occurring. 

Second, add these results together. 

 

Example Question #71 : Statistical Patterns And Random Phenomena

A basketball player makes  of his three-point shots. If he takes  three-point shots each game, how many points per game does he score from three-point range?

Possible Answers:

Correct answer:

Explanation:

First convert .

The player's three-point shooting follows a binomial distribution with  and .

On average, he thus makes  three-point shots per game.

This means he averages 12 points per game from three-point range if he tries to make 10 three-pointers per game.

Example Question #11 : Random Variables

Tim samples the average plant height of potato plants for his science class and finds the following distribution (in inches):

Which of the following is/are true about the data?

i: the mode is 

ii: the mean is 

iii: the median is 

iv: the range is 

Possible Answers:

all of the above

i & iii

i, ii & iii

i & ii

ii, iii & iv

Correct answer:

i & ii

Explanation:

Analyzing the data, there are more 6s than anything else (mode), the median is between  and     , the mean is , and the range is 

Example Question #131 : Ap Statistics

Robert's work schedule for next week will be released today.  Robert will work either 45, 40, 25, or 12 hours.  The probabilities for each possibility are listed below:

45 hours: 0.3

40 hours: 0.2

25 hours: 0.4

12 hours: 0.1

What is the mean outcome for the number of hours that Robert will work?

Possible Answers:

Correct answer:

Explanation:

We are required to find the mean outcome where the probability of each possible result varies--the random/weighted mean.  First, multiply each possible outcome by the probability of that outcome occurring.  Second, add these results together. 

 

 

Example Question #1 : How To Find Standard Deviation Of A Random Variable

We have two independent, normally distributed random variables  and  such that  has mean  and variance  and  has mean  and variance . What is the probability distribution of the difference of the random variables, ?

Possible Answers:

Normal distribution with mean  and variance .

Normal distribution with mean  and variance .

Normal distribution with mean  and variance .

Normal distribution with mean  and variance .

Correct answer:

Normal distribution with mean  and variance .

Explanation:

The mean for any set of random variables is additive in the sense that

The difference is also additive, so we have 

This means the mean of  is

The variance is additive when the random variables are independent, which they are in this case. But it's additive in the sense that for any real numbers  (even when negative), we have

.

So for this difference, we have

.

So the mean and variance are  and , respectively. In addition to that,  is normally distributed because the sum or difference of any set of independent normal random variables is also normally distributed.

Example Question #2 : How To Find Standard Deviation Of A Random Variable

If  and  are two independent random variables with  and , what is the standard deviation of the sum, 

Possible Answers:

Correct answer:

Explanation:

If the random variables are independent, the variances are additive in the sense that 

.

So then the variance of the sum is 

.

The standard deviation is the square root of the variance, so we have

.

Example Question #1 : How To Find Standard Deviation Of A Random Variable

Consider the discrete random variable  that takes the following values with the corresponding probabilities:

  •  with 
  •  with 
  •  with 

Compute the probability 

Possible Answers:

Correct answer:

Explanation:

This probability is simple to compute:

We want to add the probability that X is greater or equal to two. This means the probability that X=2 or X=3.

Adding the necessary probabilities we arrive at the solution.

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