Probability Question (Binomial RV)

Shazkar Shadowstorm

I'm a tad confused by the book and what I'm supposed to be doing for this one problem..
It says: let x be a binomial random variable with E[X]=7 and Var(X) =2.1

and then I need to find a) P{X=4} and P{X>12}

I know I need to use the binomial prob mass density function.. I'm just not sure how everything fits into it. The Var(X) part is what is confusing me specifically.

EDIT: Would I be correct in saying that E[X] = p and Var(X) = p(1-p) ? Err...

EDIT2: Can someone check if the first part would be right if I had it be (10 choose 4)(.7^6)(.3^4).. still dont know how to do part b though.

Herschel

Binomial distribution has E(X)=np and Var(X)=(1-p)np
P(X=x) = (n choose x) * ((1-p)^(n-x)) * p^x

You know E(X) and Var(X), so you can solve for n and p.

Then, you know the probability function, so you can get P(X=x) and P(X>x)