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Chapter 2--Probability

# Chapter 2--Probability - STATISTICS 301APPLIED STATISTICS...

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2f015d725c4ad66acbee1fcd46d38425ba377c77.doc STATISTICS 301—APPLIED STATISTICS, Statistics for Engineers and Scientists, Walpole, Myers, Myers, and Ye, Prentice Hall //home/vdimitrov/15961/2f015d725c4ad66acbee1fcd46d38425ba377c77.doc 4/28/2011 1

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Goal: In this section we will tackle the concept of PROBABILITY . Define: ____________________________________________________________ Interpretation of Probability: small prob _____________________________ medium prob _____________________________ large prob ________________________________ Assigning Probability—there are 3 Methods 1. The SUBJECTIVE Method Let’s find out how you feel about the question of intelligent life in the universe. a. Do you believe in life elsewhere? Yes ______ No ______ Not Sure ______ b. What do you think is the probability of intelligent life in the universe? ______ 2. The ASSUMPTION Method Answer the two questions below if the instructor rolls a six-sided die. a. The probability of getting a “2” on the top face is _________ b. What assumption did you make in answering 2a ? ________________________________________________________________ 3. The FREQUENTIST Method How would you answer the #2 if your assumption in #2 were violated? __________________________________________________________________ //home/vdimitrov/15961/2f015d725c4ad66acbee1fcd46d38425ba377c77.doc 4/28/2011 2

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1. Probability Defn Probability is a number that presents the likelihood of some event happening. Probabilities are numbersbetween 0 and 1. Sometimes they will be denoted by: decimal numbers, such as 0.04 as percentages,4%, and lastly sometimes as fractions, 4 100 . The interpretation of a probability doesnot depend on how it is written, expressed,or represented. Probabilities are interpreted as to whether an event is likely to occur or not basedon how close the probability is to zero or 1. a probability of 0 meansthe event will NEVER happen a probability of 1 meansthe event will always happen. a probability in between zero and 1 indicate that the event is less or more likely to happen depending upon how close to zero and one it is. Some Examples Suppose you flip a fair coin. The probability of getting a Head is 0.50 or 50%. If we flipped the coin once, it would not be unusual or unexpected to get a head or to not get a head . Suppose we roll a fair die—this meansthat the die has six sides and each side has the same probability of coming up. The probability of any one of the six facesof the die coming up is 1 out of 6 or about 0.1667 or 17%. Hence, when we roll this die and a “5” comes up, we should not be too surprised, since 5 is not that unusual an event.
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Chapter 2--Probability - STATISTICS 301APPLIED STATISTICS...

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