Probability Introduction

Producing DataSlide #2 A Series of Examples 1) Assume I have a box with 12 red balls and 8 green balls. If I mix the balls in the box, reach in and grab the first ball I touch, what is the probability that it is red? PR(Red) = 12/20 = 0.60

Producing DataSlide #3 THE Major Principle If … … each item has the same chance of being selected (i.e., randomization) Then, the probability is … … the number of items of interest divided by the total number of items … the proportion of interest in the population

Producing DataSlide #4 A Series of Examples 2) Suppose that we know that 45% of the Northland population is male. What is the probability that a randomly selected individual will be female? PR(female) = 0.55 =female =male

Producing DataSlide #5 A Series of Examples 3) Suppose we know that the heights of students in the Northland population is N(67,4). What is the probability that a random individual will be <60” tall? PR(< 60”) = Height

Producing DataSlide #6 A Series of Examples 4) Suppose we know that the mean heights from random samples of 16 Northland students is N(67,1). What is the probability that the mean height will be >65”? PR(> 65”) = Mean Height

Producing DataSlide #7 Remember A probability is the proportion of all items of interest as long as each item has the same chance of being selected This is why randomization is a central requirement in statistics