The discrete random variable X has the following probability distribution.
x = 1, 2. 3 for respective values of
P(X = x) = θ, 2θ, (1 – 3θ)
(a) State the range of possible values of the constant θ. 
(b) Given that E(X) = 2·2,
(i) show that θ = 0·2,
(ii) calculate the standard deviation of X,
(iii) evaluate E(1/X) . 
I should be able to do the final parts of this question, but how do I do part a]? I am at a loss for how to approach it despite it looking fairly simple. Could someone please help?