Two coins are available, one fair and the other two headed. Choose a coin and toss if once assume that the unbiased coin is chosen with probability 34. Given that the outcome is head, the probability that the two-headed coin was chosen is
P(F)=34,P(T)=1-34=14
F→ Fair coin, T→ Two headed, H→ Head occurs
∴P(T/H)=P(H/T)·P(T)P(H/T)·P(T)+P(H/F)·P(F)
[Using Baye's theorem]
=1·141·14+12·34=25