If I have set A = {1,3,5,7,9} and set B = {1,4,9}

Then could I say P(A) = 5/6 and P(B) = 1/2 ???

But if so then P(A intersect B) should be 5/6 * 1/2 = 5/12

But the actual intersection is 2/6 or 1/3. So what is wrong with this reasoning?

In the above the universal set has not been defined? Is that the problem? But can we not assume universal set is 1,3,4,5,7,9? Why does the probability theory that P(A interset B) = P(A) x P(B) not work in this case?