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Ex. 1. Find the mean 2. Find the Standard Deviation 3. Find the probability that x is within one deviation from the mean. x = possible winnings P(x)
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Warm Up • How do I know this is a probability distribution?
• What is the probability that Mary hits exactly 3 red lights?
• What is the probability that she gets at least 4 red lights?
• What is the probability that she gets less than two?
• Find the mean & standard deviation.
x=# red lights p(x)
0 0.05
1 0.25
2 0.35
3 0.15
4 0.15
5 0.05
Find Mean & Standard Deviation:
x = # books read
P(x)
0 0.131 0.212 0.283 0.314 0.07
Ex.1. Find the mean2. Find the Standard Deviation3. Find the probability that x is within one
deviation from the mean.
x = possible winnings P(x)
5 0.1
7 0.31
8 0.24
10 0.16
14 0.19
LINEAR TRANSFORMATIONSSection 6.2A
Remember – effects of Linear Transformations
• Adding or Subtracting a Constant• Adds “a” to measures of center and location• Does not change shape or measures of spread
• Multiplying or Dividing by a Constant• Multiplies or divides measures of center and location by “b”• Multiplies or divides measures of spread by |b|• Does not change shape of distribution
Adding/Subtracting a constant from data shifts the mean but doesn’t change the variance or standard deviation.
•
•
( )E X c E X c
( )Var X c Var X
Multiplying/Dividing by a constant multiplies the mean and the standard deviation.
( ) ( )E aX aE X
2( ) ( )Var aX a Var X
𝜎 𝑥 (aX )=a ∙𝜎 𝑥
Pete’s Jeep Tours offers a popular half-day trip in a tourist area. The vehicle will hold up to 6 passengers. The number of passengers X on a randomly selected day has the following probability distribution. He charges $150 per passenger. How much on average does Pete earn from the half-day trip?
# Passengers Prob
2 0.15
3 0.25
4 0.35
5 0.2
6 0.05
Pete’s Jeep Tours offers a popular half-day trip in a tourist area. The vehicle will hold up to 6 passengers. The number of passengers X on a randomly selected day has the following probability distribution. He charges $150 per passenger. What is the typical deviation in the amount that Pete makes?
# Passengers Prob
2 0.15
3 0.25
4 0.35
5 0.2
6 0.05
What if it costs Pete $100 to buy permits, gas, and a ferry pass for each half-day trip. The amount of profit V that Pete makes from the trip is the total amount of money C that he collects from the passengers minus $100. That is V = C – 100. So, what is the average profit that Pete makes? What is the standard deviation in profits?
A large auto dealership keeps track of sales made during each hour of the day. Let X = the number of cars sold during the first hour of business on a randomly selected Friday. Based on previous records, the probability distribution of X is shown below. Suppose the dealership’s manager receives a $500 bonus from the company for each car sold. What is the mean and standard deviation of the amount that the manager earns on average?
# cars sold Prob
0 0.3
1 0.4
2 0.2
3 0.1
Suppose the dealership’s manager receives a $500 bonus from the company for each car sold. To encourage customers to buy cars on Friday mornings, the manager spends $75 to provide coffee and doughnuts. Find the mean and standard deviation of the profit the manager makes.
# cars sold Prob
0 0.3
1 0.4
2 0.2
3 0.1
Variance of y = a + bx• Relates to slope.
22
2
2 2 2
2
2 2 2
var( ) var( )
y x
ybxybx
y b x
y b x
b
Effects of Linear Transformation on the Mean and Standard Deviation if .
=
*Shape remains the same.
Example: Three different roads feed into a freeway entrance. The number of cars coming from each road onto the freeway is a random variable with mean values as follows. What’s the mean number of cars entering the freeway.
RoadMean #
Cars
1 800
2 1000
3 600
Mean of the Sum of Random Variables
+
For any two random variables, X and Y, if then the expected value of T is
Ex: What is the standard deviation of the # of cars coming from each road onto the freeway.
RoadMean #
CarsSt. Dev.
1 800 34.5
2 1000 42.8
3 600 19.3
Variance of the Sum of Random Variables
For any two random variables, X and Y, if then the variance of T is
Mean st devx 20 5y 24 3
x y
3 2x y
Mean st devx 20 5y 24 3
x y
3x y
Mean st devx 20 5y 24 3
x y
3 2x y
Mean st devx 20 5y 24 3
x y
3x y
Find: and 3 2x y 3 2x y
x P(x) y P(y)3 0.32 10 0.224 0.14 20 0.345 0.12 30 0.186 0.42 40 0.26
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