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Probability and Statistics Exam 1, Fall 2006, Exams of Statistics

An answer key for exam 1 of stat 205, a probability and statistics course, held in fall 2006. It includes solutions for various probability problems, such as calculating probabilities of intersections, unions, and conditional probabilities, as well as problems related to mean, median, standard deviation, and normal distribution.

Typology: Exams

2012/2013

Uploaded on 02/26/2013

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STAT 205 Name:__ANSWER KEY______________
Fall 2006
Exam 1
s2 =
)1(
)( 2
1
n
yyi
n
i
P{E1 U E2} = P{E1} + P(E2} P{E1 ∩ E2}
P{E1 ∩ E2} = P{E1}P{E2| E1}
μY = ∑yi P{Y = yi}
σY2 = ∑(yi μY)2 P{Y = yi}
= E(Y2) (E(Y))2
P{Y = j} = nCj pj (1 p)n-j
μY = np
σY2 = np(1 p)
Z =
)( Y
pf3
pf4
pf5

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STAT 205 Name:__ANSWER KEY______________ Fall 2006 Exam 1

s^2 = ( 1 )

( )^2 1 

n

yi y

n i

P{E 1 U E 2 } = P{E 1 } + P(E 2 } – P{E 1 ∩ E 2 }

P{E 1 ∩ E 2 } = P{E 1 }P{E 2 | E 1 }

μY = ∑yi P{Y = yi}

σY^2 = ∑(yi – μY)^2 P{Y = yi} = E(Y^2 ) – (E(Y))^2

P{Y = j} = (^) nCj pj^ (1 – p)n-j μY = np σY^2 = np(1 – p)

Z =

( Y )

Part I: Answer six of the following seven questions. If you complete more than six, I will grade only the first six. Five points each.

  1. P(A) = 0.2 P(B) = 0.40 A and B are independent. What is P(A∩B)?

(0.2)(0.4) = 0.

  1. P(A) = 0.2 P(B) = 0.40 A and B are mutually exclusive. What is P(AB)?

0.2 + 0.4 = 0.

  1. P{A} = 0.8 P{A B} = 0.2 What is the probability of B given A?

  2. Circle the correct answer. In a breeding experiment, white chickens with small combs were mated and produced 190 offspring. Researchers observed the offspring to determine whether the offspring had White feathers, small comb White feathers, large comb Dark feathers, small comb Dark feathers, large comb

The variable in this study is discrete / continuous / nominal / ordinal.

  1. The following data set is weight gain (lbs.) in lambs fed a certain diet over a specified amount of time: 9, 16, 21, 11, 18

Calculate the mean of this data.

Calculate the median of this data.

M = Q 2 = 16 pounds

Part II: Answer every part of the next two problems. Read each question carefully, and show your work for full credit.

  1. In the United States, 11% of adolescent girls have iron deficiency. Suppose six adolescent girls are chosen at random.

a) (15 pts.) Find the probability that at most one of these six girls will be iron deficient.

Using the TI-83/ P(Y  1 ) = binomcdf(6, 0.1 1 , 1 ) = 0.

b) (15 pts.) Find the probability that 2 or more of these girls will be iron deficient. P(Y  2 ) = 1 – P(Y  1 ) = 1 – binomcdf(6, 0.1 1 , 1 ) = 0.

  1. The brain weights of a certain population of adult Swedish males follow a normal distribution with mean μ = 1400g and standard deviation σ = 100g.

a) (15 pts.) What percentage of the brain weights for this population are between 1200 and 1600 grams?

normalcdf(1200, 1600, 1400, 100) = 0.9545  95.45%

b) (15 pts.) What is the 80th^ percentile for this distribution?

invNorm(0. 8 , 1400, 100) = 1484.162 grams