Probability & Statistics with R for Engineers and Scientists
Probability & Statistics with R for Engineers and Scientists
1st Edition
ISBN: 9780321852991
Author: Michael Akritas
Publisher: PEARSON
Question
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Chapter 2.5, Problem 10E

(a)

To determine

Find the probability that the sample contains no defective fuses.

(a)

Expert Solution
Check Mark

Answer to Problem 10E

The probability that the sample contains no defective fuses is 0.467.

Explanation of Solution

Calculation:

The conditional probability for any two events A, B with P(A)>0,

P(B|A)=P(AB)P(A)

Let D1 denotes the first is defective, and D2 denotes second is defective.

A batch of 10 fuses contains three defective ones.

The probability that the first one is defective is,

P(D1)=310

The probability that the first one is not defective is,

P(D1c)=710

The probability that the second is defective given that first is defective is,

P(D2|D1)=29

The probability that the second is not defective given that first is not defective is,

P(D2c|D1c)=69

The probability that the second is not defective given that first is defective is,

P(D2c|D1)=79

The probability that the sample contains no defective fuses is,

P(no defective)=P(D2cD1c)=P(D2c|D1c)P(D2c)=69×710=0.467

Hence, the probability that the sample contains no defective fuses is 0.467.

(b)

To determine

Find the probability mass function of X.

(b)

Expert Solution
Check Mark

Answer to Problem 10E

The probability mass function of X is,

X012
Probability0.4670.4660.067

Explanation of Solution

Calculation:

The formula for complement of event A is,

P(Ac)=1P(A)

Let X denotes the random variable denoting the number of defective fuses in the sample.

The probability that the sample contains no defective fuses is,

P(no defective)=P(D2cD1c)=P(D2c|D1c)P(D2c)=69×710=0.467

The probability that the sample contains defective fuses is,

P(X=2)=P(D2D1)=P(D2|D1)P(D1)=29×310=0.067

The probability that the sample contains one defective fuse is,

P(X=1)=1P(X=0)P(X=2)=10.4670.067=0.466

Hence, the probability mass function of X is,

X012
Probability0.4670.4660.067

(c)

To determine

Find the probability that the defective fuse was the first one selected given that X=1.

(c)

Expert Solution
Check Mark

Answer to Problem 10E

The probability that the defective fuse was the first one selected given that X=1 is 0.5.

Explanation of Solution

Calculation:

Bayes’ theorem:

The Bayes’ formula is,

P(Aj|B)=P(Aj)P(B|Aj)i=1kP(Ai)P(B|Ai)    for j=1,2,,k.

The probability that the defective fuse was the first one selected given that X=1 is,

P(D1|X=1)=P(D1D2c)P(X=1)=P(D2c|D1)P(D1)P(X=1)=(79×0.3)0.466=0.2330.466

                      =0.50

Hence, the probability that the defective fuse was the first one selected given that X=1 is 0.5.

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