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Week 5 Lecture, Statistics for Decision Making
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Week 5 Lecture Statistics for Decision
MakingB. Heard
These charts are not to be posted or used without my written permission. Students can download a copy for their personal use.
Preparing for the Week 5 Quiz◦ Factorials◦ Combinations/Permutations◦ Probability◦ Probability Distributions◦ Discrete/Continuous Distributions◦ Binomial Distribution◦ Poisson Distribution◦ Pivot Tables
Week 5 Lecture
Factorials◦ n! simply means n x (n-1) x (n-2) x …. 3 x 2 x 1
For example 5! = 5x4x3x2x1 = 120, so 5!=120 Always remember that 0! = 1 (NOT ZERO) Additional examples
3! + 4! = (3x2x1) + (4x3x2x1) = 6 + 24 = 30 5(5-3)! = 5 x 2! = 5 x (2x1) = 5x2 = 10 5(5! – 3!) = 5(120 – 6) = 5(114) = 570 4!(0!) = 24(1) = 24 3!/0! = 6/1 = 6
Week 5 Lecture
Combinations/Permutations◦ Combinations – The number of ways of something
happening when order DOES NOT matter.
◦ Permutations – The number of ways of something happening when order DOES matter.
◦ The number of ways to pick 5 out of 10 players to start on a basketball team would be a combination.
◦ The number of ways to pick 5 out of 10 players to play 5 different positions would be a permutation.
Week 5 Lecture
Combinations/Permutations (continued)◦ The number of ways to pick 3 committee members
out of 11 people would be a combination because there are not distinct positions mentioned (order doesn’t matter).
◦ The number of ways to pick 3 committee members out of 11 people where 1 would be the President, Vice-President and Treasurer would be a permutation because there are distinct positions mentioned (order does matter, you not only could be picked, but you could be one of three different positions).
Week 5 Lecture
Combinations/Permutations (continued) Let’s Do these in Minitab
◦ The number of ways to pick 3 committee members out of 11 people would be a combination because there are not distinct positions mentioned (order doesn’t matter). This is a combination where we are picking 3 from 11 (Sometimes noted
11C3).
◦ The number of ways to pick 3 committee members out of 11 people where 1 would be the President, Vice-President and Treasurer would be a permutation because there are distinct positions mentioned (order does matter, you not only could be picked, but you could be one of three different positions). This is a permutation where we are picking 3 from 11 (Sometimes noted
11P3).
Week 5 Lecture
Combinations/Permutations (continued) Minitab
◦ Let’s look at the combination where we are picking 3 from 11 (Sometimes noted 11C3).
In Minitab, Choose “Calc”, then “Calculator” Type C1, or any other blank column in the “Store result in variable” box In the Expression box, type “Combinations(11,3)”
In the cell you chose, you will see your answer of 165 This means there are 165 ways to pick a committee of 3
from 11 people (remember order didn’t matter).
Week 5 Lecture
Combinations/Permutations (continued) Minitab
Week 5 Lecture
Combinations/Permutations (continued) Minitab
◦ Let’s look at the permutation where we are picking 3 from 11 (Sometimes noted 11P3).
In Minitab, Choose “Calc”, then “Calculator” Type C1, or any other blank column in the “Store result in variable” box In the Expression box, type “Permutations(11,3)”
In the cell you chose, you will see your answer of 990 This means there are 990 ways to pick a committee of 3
from 11 people where there are THREE DISTINCT POSITIONS (order DID matter).
Week 5 Lecture
Combinations/Permutations (continued) Minitab
Week 5 Lecture
Week 5 Lecture Combinations/Permutations (continued)
For the same numbers, the number of permutations will always be larger! This is because there are distinct positions.
As an example3C3 = 1 (there is only one way to pick three from three)3P3 = 6 (there are 6 ways to pick 3 people from 3 to serve in 3
distinct positions, think about it 3 could be President, 2 are left to serve as Vice-President, one is left to serve as Treasurer, 3x2x1 = 6
In our previous example we had 11P3 = 990 which could be looked at as 11 x 10 x 9 = 990. Why? 11 could be Pres., 10 VP, and 9 Treasurer.
Probability◦ Probability is simply the number of desired events
over the total number of events that can happen. Sound complicated? It’s not What is the probability of rolling a 5 on six-sided die? One side with a five/six sides = 1/6
Week 5 Lecture
Probability (continued)◦ Sample Spaces (What can happen?)
For a regular light switch, the sample space would be {on, off}
For a six-sided die, the sample space would be {1,2,3,4,5,6}
For a new baby, the sample space would be {girl, boy}
For suits in a card deck, the sample space would be {hearts, diamonds, clubs, spades}
Week 5 Lecture
Probability (continued)◦ Examples
What is the probability of drawing a Jack from a standard deck of cards? (There are 4 cards out of the 52 that are Jacks) The probability would be 4/52 or 1/13 simplified
What is the probability of drawing a red Jack from a standard deck of cards? (There are 2 cards out of the 52 that are red Jacks) The probability would be 2/52 or 1/26 simplified
What is the probability of drawing a Jack of Hearts from a standard deck of cards? (There is only 1 Jack of Hearts out of the 52) The probability would be 1/52
Week 5 Lecture
Probability (continued)◦ Conditional Probability Examples
What is the probability of drawing a Jack from a standard deck of cards, if you first drew a 3 of clubs and didn’t replace it? (There are 4 cards out of the 51 that are Jacks) The probability would be 4/51 (Remember you didn’t replace the 3 of clubs)
What is the probability of drawing a Jack from a standard deck of cards, if you first drew a Jack of clubs and didn’t replace it? (There are 3 Jacks left out of the 51) The probability would be 3/51 or 1/17 simplified (Remember you didn’t replace the Jack of clubs)
Week 5 Lecture
Probability Distributions◦ All Probabilities must be between 0 and 1and the
sum of the probabilities must be equal to 1.
◦ Examples◦ If X = {5, 10, 15, 20} and P(5) = 0.10, P(10) =
0.20, P(15) = 0.30, and P(20) = 0.40, can the distribution of the random variable X be considered a probability distribution? YES, because all probabilities (0.10,0.20,0.30,0.40)
are between 0 and 1 and they add up to 1 (0.10+0.20+0.30+0.40 = 1)
Week 5 Lecture
Probability Distributions (continued)◦ Examples◦ If X = {5, 10, 15, 20} and P(5) = 0.20, P(10) =
0.20, P(15) = 0.20, and P(20) = 0.20, can the distribution of the random variable X be considered a probability distribution? No, the probabilities (0.20,0.20,0.20,0.20) are
between 0 and 1 BUT they DO NOT add up to 1 (0.20+0.20+0.20+0.20 = 0.80)
Week 5 Lecture
Probability Distributions (continued)◦ Examples◦ If X = {-5, A, 7, 0} and P(-5) = 0.50, P(A) = 0.10,
P(7) = 0.10, and P(0) = 0.30, can the distribution of the random variable X be considered a probability distribution? YES, the probabilities (0.50,0.10,0.10,0.30) are
between 0 and 1 and they add up to 1 (0.50+0.10+0.10+0.30 = 1)
{-5, A, 7, 0} Does Not matter, you can have negative numbers, letters, colors, names, etc. in the sample space but you couldn’t have negative values as PROBABILITIES
Week 5 Lecture
Probability Distributions (continued)◦ Examples◦ Given the random variable X = {100, 200} with
P(100) = 0.7 and P(200) = 0.3. Find E(X).
◦ Simple
◦ E(X) = Sum of X(P(X) (add the values times their probabilities)
◦ E(X) = 100(0.7) + 200(0.3) = 70 + 60 = 130
Week 5 Lecture
Probability Distributions (continued)◦ Examples of Probability values◦ Which of these can be probability values?◦ 3/5 YES◦ 0.004 YES◦ 1.32 NO◦ 43% YES◦ -0.67 NO◦ 1 YES◦ 5 NO◦ 0 YES
Week 5 Lecture
Discrete/Continuous Distributions Simple explanation A discrete probability distribution has a finite
number of possible outcomes. (People, items, distinct things that can not be measured infinitesimally)
A continuous probability is based on a continuous random variable such as a persons height or weight. (GOOD EXAMPLES ARE UNITS OF MEASURE LIKE HEIGHTS, WEIGHTS, VOLUME, ETC.)
Week 5 Lecture
Discrete/Continuous Distributions Simple Example
◦ The number of cans of soda in your refrigerator is discrete (0,1,2,3 etc.)
◦ The amount of soda IN the can is continuous (ounces can be split and split and split, etc.)
Week 5 Lecture
Binomial and Poisson DistributionsKnow the difference between the two!
A good hint is that a Poisson usually give you an average number of something per time period and a Binomial gives you a probability and a number of times/trials/etc.
Week 5 Lecture
Binomial Distribution using Minitab
The way is to show you an example.
Let’s say we have a binomial experiment with p = 0.2 and n = 6 and you are asked to set up the distribution and show all x values and the mean, variance and standard deviation.
Week 5 Lecture
Binomial Distribution using Minitab ◦ Open a new Minitab Project◦ Since n= 6, put 0,1,2,3,4,5,6 in column C1 (Don’t
forget the zero)◦ Go to Calc>>Probability Distributions>>Binomial◦ Change Radial Button to “Probability”◦ Put 6 in for number of trials and 0.2 in for event
probability◦ Put “C1” in for Input Column◦ Click “OK”
Week 5 Lecture
Binomial Distribution using Minitab
Week 5 Lecture
You would writeX = {0,1,2,3,4,5,6}P(x=0) = 0.2621
P(x=1) = 0.3932
P(x=2) = 0.2458
P(x=3) = 0.0819
P(x=4) = 0.0154
P(x=5) = 0.0015
P(x=6) = 0.0001
This is your distribution, we now have to calculate the mean, variance and standard deviation.
Etc.
Binomial Distribution using Minitab ◦ Remember we had p = 0.2 and n = 6◦ Mean?
E(X) = np so E(X) = 6(0.2) = 1.2 (the mean) Why “E(X)”? Because we would “expect” the outcome
1.2 times out of the 6 times we did it.◦ Variance?
V(X) = npq (q is just “1-p”), so V(X) = 6(0.2)(1-0.2) = 6(0.2)(0.8) = 0.96 (the variance)
◦ Standard Deviation? Std Dev. = Square Root of the Variance = √0.96 =
0.9216 (the standard deviation)
Week 5 Lecture
Binomial Distribution using Minitab◦ Same Example, what if you were asked◦ P(X≥5)◦ P(X<3)◦ Etc.◦ Use your probabilities (next page)
Week 5 Lecture
Binomial Distribution using Minitab◦ P(X≥5)
Week 5 Lecture
P(X≥5) = P(X=5) + P(X=6) = 0.001536 + 0.000064 = 0.0016
Binomial Distribution using Minitab◦ P(X<3)
Week 5 Lecture
P(X<3) = P(X=0) + P(X=1) + P(X=2) = 0.262144 + 0.393216 = 0.245760 = 0.90112
Poisson Distribution with Minitab
Week 5 Lecture
Probability Density Function
Poisson with mean = 5
x P( X = x )3 0.140374
Poisson Distribution using Minitab Go to Calc>>Probability Distributions>>PoissonChange Radial Button to “Probability”Put 5 in for number of trials and 3 in for “Input Constant”Click “OK”
Find P(x=3)For a Poisson Distribution with mean = 5
Poisson Distribution with Minitab
Week 5 Lecture
What is the probability that X≤3? Use Cumulative Distribution Function
Poisson with mean = 5
x P( X <= x )3 0.265026
Pivot Tables
Week 5 Lecture
Chocolate Vanilla Total
Girls 13 6 19
Boys 17 5 22
Total 30 11 41
Pivot Tables
Week 5 Lecture
Chocolate Vanilla Total
Girls 13 6 19
Boys 17 5 22
Total 30 11 41
Find P(Girl)P(Girl) = 19/41
Find P(Vanilla)P(Vanilla) = 11/41
Find P(Girl who likes Chocolate)
13 out of the 41 so it is 13/41
Pivot Tables
Week 5 Lecture
Chocolate Vanilla Total
Girls 13 6 19
Boys 17 5 22
Total 30 11 41
Find P(Girl given they like chocolate)P(Girl|Choc) = 13/30
Find P(Like Vanilla given they are a boy)P(Vanilla|Boy) = 5/22
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Week 5 Lecture