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For a discrete random variable X with the following pdf find it's expectation. X : -3 4 7 12

p(x) : 0.35 0.25 0.3 0.1

I am trying to study and understand how this problem works so I can apply it on my test on Friday, however I am not sure how to go about this problem. Any help with the answer so I can check my work is greatly appreciated.

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    Have a look [here](https://en.wikipedia.org/wiki/Expected_value#Univariate_discrete_random_variable.2C_finite_case). Btw, you are not dealing here with a [pdf](https://en.wikipedia.org/wiki/Probability_density_function) but with a [pmf](https://en.wikipedia.org/wiki/Probability_mass_function). – 2017-02-07

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For a discrete distribution, the expectation (average) is given by $$ E(X) = \sum_x x p(x)$$ so in your case it is $$ E(X) = (-3)*0.35+ 4*0.25+7*0.3+12*0.1.$$