Question

When an opinion poll calls a residential telephone number at random, there is only a 20% chance that the call reaches a live person. You watch the random digit dialing machine make 15 calls. Let X = the number of calls that reach a live person. Find and interpret
\sigma_X
σ X
​

Answer 1

The interpret μ$_x$ = 3 and the interpret σ$_x$ = 1.5492 .

Given :

When an opinion poll calls a residential telephone number at random, there is only a 20% chance that the call reaches a live person. You watch the random digit dialing machine make 15 calls. Let X = the number of calls that reach a live person.

here n = 15 and p = 0.20

μ$_x$ = n * p

= 15 * 0.20

= 3

Standard deviation σ$_x$ = $\sqrt{n * p ( 1- p )}$

= $\sqrt{15 * 0.20 ( 1- 0.20)}$

= 1.5492

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