Final answer:
The probability of picking a black marble first and then picking another black marble is 4/9.
Step-by-step explanation:
To find the probability of picking a black marble first, putting it back in the bag, and then picking a black marble, we multiply the probabilities of each individual event.
The probability of picking a black marble from three marbles, where two are black, is 2/3.
Since we put the black marble back in the bag, the probability of picking another black marble remains the same, which is also 2/3.
Therefore, the probability of picking a black marble first and then picking another black marble is (2/3) * (2/3), which simplifies to 4/9.