Possibility of two cards will come by the river

[AncientPC]

Assuming no Jacks in your hand, how do you calculate the probability that there will be 2 Jacks on the table by the river?

[Tom1975]

There are 50 unknown cards, therefore there are C(50,5) possible boards. There are C(4,2) ways to choose the two jacks and C(46,3) ways to choose the other three cards, so your answer is C(4,2)*C(46,3)/C(50,5)=0.042987408.

Note that this solution is for boards with exactly two jacks, not three or four.