Math question in probability!?

[alex]

If I am throwing a coin four times, what is the chance that it will land on heads two times? And how does the proper calculation look like?


Yes, I know the answer is 6/16, but how does one calculate it?

Thanks in advance!

 

[wats up?]

nCr p^r q^n-r

4C2 (1/2)^2 (1/2)^2

Equals 6/16