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This is an example from the text I'm using but I just want to make sure that I'm not going crazy here.

A multiple choice exam consists of 25 questions each with five choices with once choice is correct. Randomly select an answer for each question. Let X be the random variable representing the total number of correctly answered questions.

(c) Find the expected value of the number of correct answers.

a and b are inconsequential, my issue is with (c).

The expected value is just $n*p$ is it not? The answer in the book says it is $(25)(0.2)(.8)$ but that makes absolutely no sense to me as that is the variance, not the expected value.

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    E(x) = n*p which for your example is 5 – 2017-02-26
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    Alright, so then the text is wrong. This is what I thought, but I wasn't sure. Thank you! – 2017-02-26
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    you can also use sum of (r * p(x=r)) which ought to give the same thing as a double check – 2017-02-26
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    The answer book has given the Variance not the Mean – 2017-02-26

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