Students A, B and C are discussing the solution of a Problem from their home assignment in "Statistics". The

solution is given by one of their colleagues. Student A will say the solution is false if and only if either B or C say

they have found a mistake in the solution. Neither of B and C have had time to go through the solution, but B will

randomly with a 50% probability say that he has found a mistake. C will wait to hear what B says, but if B does

not say he has found a mistake, then C will randomly with a 20% probability say that he has found a mistake in

the solution. What is the probability that B said he found a mistake if A says the solution is false?