A box has 4 dice in it. 4 of them are fair and one of them is marked with 5 on all its faces. A dice chosen at random and rolled thrice shows 5 on all the occasions. The probability that the die chosen was a biased one is?
216/219
Let X: Die shows up number 5
Y:It is an unfair die=14
Z:it is a normal die=34
P(XY)=1
P(XZ)=1216
P(YX)=14×1(14×1+34×1216)=216219