I believe the answer would be 36/400, 9/100, or 9%
(I believe you are asking for the probability of picking blue then another blue )
So, in the jar, there are 20 marbles, 6 of which are blue, so pick one would be a 6/20 or 3/10 ≈ 33.3%
Assuming that you grabbed a blue marble then it was replaced with another blue marble, you would multiply 6/20 and 6/20 (the individual chances of getting one blue) and get 36/400, which simplifies to 9/100 or 9%
Please correct me if I am wrong, have a good day!
