Need help on these types of statistics problems

Test Preparation AP Test Preparation
1

<p>There are 10 calculators, two are defective, and you choose two calculators. What is the probability that you choose exactly 1 defective calculator</p>

2

<p>Is the answer 0.18?</p>

3

<p>Nevermind I was wrong, observations aren’t independent.</p>

4

<p>aright thanks man, somebody told me .32 was the right answer but i had no idea how to get it</p>

5

<p>Yes, it’s 0.32. I did my math wrong. It’s a binomial distribution with p=0.2.</p>

6

<p>I got .18 as well.</p>

<p>Probability of success the first time = .2
Probability of failing the second time = 1 - (1/9)</p>

<p>Multiply both for .1777777778</p>

7

<p>I also initially thought it was binomial but i remembered that in a binomial distribution observations must be independent.</p>

<p>Picking a calculator changes the probability of picking a second, so its not independent.</p>

8

<p>They are independent.</p>

<p>Since it follows Bernoulli trial, p = 2/10 = 0.2. You’re choosing two calculators, it means two trials. Since it asks for the probability of EXACTLY one, you use binomPdf.</p>

<p>binompdf(2, 0.2, 1) = 0.32</p>