The random variable X has the distribution B (n, 0.1). Given that the mean and standard deviation of X are equal, find the value of n. 
The only things I could work out were:
E(X)(mean) = n x 0.1
SD(X) = root of VAR(X)
VAR(X) = n x 0.1 x 0.9
VAR(X) = n x 0.09
n x 0.1 = root of 0.09 x n
What happens from here? Is it meant to be solved in a different way?