# Math Help - Defects of bottle selection

1. ## Defects of bottle selection

Approximately 10% of the glass bottles coming off a production line have serious defects in the glass. Two bottles are randomly selected for inspection. Find the expected value and the variance of the number of inspected bottles with serious defects.

$p=.10, \ \ \bar{p}=.90$

I am not sure how you use this information to find the expected value.

2. when two bottles are randomly selected, there may be either no bottles with serious defect, or there may be one bottle with serious defect, or there may be both bottles with serious defect.

You can use binomial distribution to find P(X=0), P(X=1), and P(X=2), and then calculate the mean and variance

3. Originally Posted by dwsmith
Approximately 10% of the glass bottles coming off a production line have serious defects in the glass. Two bottles are randomly selected for inspection. Find the expected value and the variance of the number of inspected bottles with serious defects.

$p=.10, \ \ \bar{p}=.90$

I am not sure how you use this information to find the expected value.
$\displaystyle n= 2, p= 0.1$

$\displaystyle E(X) = n\times p , Var(X) = np(1-p)$