Probability that A speaks truth is $\large \frac{4}{5} $ . A coin is tossed. A reports that a head appears. The probability that actually there was head is?

Question

\[ \begin{array} ((A) \frac{4}{5} \quad & (B) \frac{1}{2} \quad & (C) \frac{1}{5} \quad & (D) \frac{2}{5} \end{array} \]