Solution: From the meaning of the question, ∫S = {1, 2,3,4,5,6}, event A = {2,3,5}, event B={ 1, 2,4,5,6},

∴ Event AB = {2 2,5},

∴ p (ab) = No.26,

∫p(b)= 5 6∴p(a|b)=p(ab)p(b)= 2 6 5 6 = 2 5

So the answer is: 2 5.