Probability of exactly two heads in four coin flips? 
When you flip a coin four times, what is the probability that it will come up heads 
  exactly twice?   

My calculation: 


*

*we have $2$ results for one flip : up or down 

*so flip $4$ times, we have $4\cdot2 = 8$ results total 


Thus the probability is: $2/ 8 = 0.25 $
but the correct answer is $0.375$. Can anyone explain why I'm wrong?

Assuming unbiased coin with probability of head $=\dfrac12$
and using Binomial Distribution, $$\binom42\left(\frac12\right)^2\left(1-\frac12\right)^{4-2}$$
