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Chapter 6: Q. 81 (page 404)

81. Random digit dialing When an opinion poll calls residential telephone numbers at random, only20% of the calls reach a live person. You watch the random digit dialing machine make 15 calls. Let X= the number of calls that reach a live person.
(a) Find and interpret 渭X.
(b) Find and interpret 蟽X.

Short Answer

Expert verified

(a) The interpret 渭Xis 3.

(b) The interpret 蟽X is 1.5492.

Step by step solution

01

Part (a) Step 1: Given information 

An opinion poll calls residential telephone numbers at random, only 20%of the calls reach a live person. And the random digit dialing machine make15 calls.

02

Part (a) Step 2: Explanation 

Given: n=15, and p=0.20

The mean of the size nand the probability pis:

渭x=n脳p

=15(0.20)

=3.

03

Part (b) Step 1: Given information 

Let X= the number of calls that reach a live person.

04

Part (b) Step 2: Explanation 

Given: n=15and p=0.20

The standard deviation is:

蟽x=(n脳p)(1-p)

=15(0.20)(1-0.20)

=1.5492.

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