Let X1 and X2 be a random sample from B(n,p). Compute the mean and the variance of X1+X2.
Can anyone help with this one as well?
For the variance :
If X1 and X2 are independent, then cov(X1,X2)=0
After that, you have several other means, using probability density functions, moment generating functions, etc... But I don't know what you can use...