Help with a stat problem.

Test Preparation
1

<p>Most sample surveys use random digit dialing equipment to call residential telephone numberse at random. The telephone polling firm Zogby International reports that the probability that a call reaches a live person is 0.2. Calls are independent.</p>

<p>a. A polling firm places 5 calls. What is the probability that none of them reaches a person?</p>

<p>This is what I did: 1- .2^5=.99968
On the other hand, this is what the book did: .8^5=.32768</p>

<p>I don't see why the way I did it doesn't work. Any help?</p>

2

<p>you are trying to see the probability of NOT getting a live person the first time, then NOT getting one a second time, then NOT a third, fourth, etc. The probability of getting someone is .2, therefore, probability of NOT getting someone is .8. If you want to NOT get someone 5 times in a row, you need to multiply .8 by itself 5 times.</p>

<p>.8^5</p>

<p>What you are doing is subtracting .2^5 from 1 which doesn't seem to make much sense to me</p>

3

<p>I think you meant to do
(1-.2)^5
that should work the same.</p>

4

<p>oh, how stupid of me. haha thx legend and zante.</p>

5

<p>I think he's trying to do ..
Total = None reach + reach
Total - reach = None reach
1 - (.2^5) = none reach</p>

<p>And umm, it doesn't work.</p>