(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Given a 30% failure rate, what is the mean number of students who fail, and what is the variance? There are 8 students in the course.

2. Relevant equations

I think these are the correct equations:

Mean = Probability * Number of students

Variance = Sum from i=1 to 8 of p_{i}(x_{i}-Mean)^2

3. The attempt at a solution

So using the Mean formula I got 0.3*8=2.4

Using the variance formula I got

(0.3)(1-2.4)^{2}+(0.3)(2-2.4)^{2}+(0.3)(3-2.4)^{2}+(0.3)(4-2.4)^{2}+(0.3)(5-2.4)^{2}+(0.3)(6-2.4)^{2}+(0.3)(7-2.4)^{2}+(0.3)(8-2.4)^{2}

which is approximately equal to 23.184 (see variance formula here: wolfram alpha, then click approximate form )

Do I then square root to find the actual variance?

Thanks for any help!

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# Homework Help: Calculating mean and variance of probability

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