All AP Statistics Resources
Example Questions
Example Question #3 : Random Variables
Which of the following would be considered a binomial experiment?
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
Predicting the probability that in a series of ten games of Rock, Paper, Scissors played with random strategy, one individual obtains six victories
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?
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
The number of times heads comes up on 10 coin flips
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?
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?
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?
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
all of the above
i & iii
i, ii & iii
i & ii
ii, iii & iv
i & ii
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?
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, ?
Normal distribution with mean and variance .
Normal distribution with mean and variance .
Normal distribution with mean and variance .
Normal distribution with mean and variance .
Normal distribution with mean and variance .
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,
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 .
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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