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# Discete random variable help! watch

1. I have this question that I've been trying to do but I just won't get the same answer as what my teacher gave us, please could someone show me how to they would do this Q :

The random variable X has the distribution below. Given Var(x)= 0.75, find the values of a and b.

x= 1 2 3
P(X=x) = a b a

Thank you
2. (Original post by rn123)
I have this question that I've been trying to do but I just won't get the same answer as what my teacher gave us, please could someone show me how to they would do this Q :

The random variable X has the distribution below. Given Var(x)= 0.75, find the values of a and b.

x= 1 2 3
P(X=x) = a b a

Thank you
Does a = 0.375 b = .25?

If so, can you write down straight away what E(X) is?

Then you need two equations for a and b. One comes from using the variance formula. The other can come from knowing what the probabilities must add up to.

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Updated: February 4, 2016
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