Suppose you have two coins which appear identical in your pocket.you know that one is fair and one is 2 headed.If you take one out,toss it and get a head,what is the probability that it was a fair coin?

Question

$\begin{array}{1 1} \frac{1}{3} \\ \frac{2}{3} \\ \frac{1}{2} \\ \frac{3}{4} \end{array} $