AP STATS Chapter 15

probabilities must sum to

1

Discrete Random variable

A finite or countable variable, like the number of questions on a test or the number of desks in a classroom.

Probability Model

A probability model has two parts: the collection of all possible values and the probability that they occur.

Random Variable

A variable whose outcome relies on some random event.

expected value formula

E(x)=(p1*X1)+(p2*X2)... take each x value and multiply it by its probability, then add it to the next value multiplied by its probability....

Continuous Random variable

Infinite or measured, like the distance a ball is thrown or the MPG of a car.

combining variables

Mean of the total= mean 1+mean 2 Mean of the difference= Mean 1- Mean 2 The variance of the total and the varience of the differences are both st dev^2+ stdev^2 since variences only add St Deviations are found by adding the variences and takin gtheir square root becuase st. dev cannot be added, onlu variences/

expected value

the log run average is the average number of anythings per anything if we take many samples.

standard deviation

the square root of the variance.

If normality is known

then combined variables will follow a normal model, allowing you to use z scores to find their probabilities.

Variance formula

variance= (x value- expected value)^2 * P(X value) +....

A large variance indicates a

wide spread

variance

a measure of spread that is related to the standard deviation.

a small variance indicates

that the data is not very spread out.