# Math Help - Mean, Variance, and Standard Deviation

1. ## Mean, Variance, and Standard Deviation

x ------ 1 ------- 2 -------3-------- 4------ 5
P(X=x) .18----- .22 -------.35------ a ------.13

need some help in solving this
not the answer jus the steps

a=.12

find the value of a
find the mean of the random variable X
find the value of the E(X^2)
find the variance the the random variable X
find the standard deviation of the random variable X

2. Originally Posted by math321
x ------ 1 ------- 2 -------3-------- 4------ 5
P(X=x) .18----- .22 -------.35------ a ------.13
Mean is $E(x) = \sum\limits_x {x \cdot \mathcal{P}(x)}$
Likewise, $E(x^2) = \sum\limits_x {x^2\cdot \mathcal{P}(x)}$