p(3h/2h) = p(3h,2h)/p(2h) p(3h,2h) = p(3h) = (1/3)1 + (1/3)(1/2)(1/2)(1/2) p(2h)= (1/3)1 + (1/3)(1/2)(1/2)

where the 1/3 is prob of each coin and 1/2 is prob of head and tail. answer is 9/10 according to me.