Answer:6/7
Explanation:
so basically given observation is u got a tail from a biased coin.
so our favorable case is getting a tail from biased coin.
we will use the probability for it:
p1= probability of getting choosing biased coin and getting tail =probability of choosing biased coin* probability of tail = 3/4*1
p2= probability of choosing a fair coin and getting tail= probability of choosing fair coin*probability of getting tail on it = 1/4*1/2 = 1/8
so p(E)= p1/(p1+p2)= 3/4/(3/4+1/8)=7/8