A bag holds 4 red, 3 blue and 5 green marbles.

Step 1. Put back. $\dfrac{3}{12} \times \dfrac{3}{12} = \dfrac{1}{16} = 0.0625$.

Step 2. Not put back. $\dfrac{3}{12} \times \dfrac{2}{11} = \dfrac{6}{132} = 0.0455$.

Step 3. Why smaller. Once a blue marble is out, a second blue one is less likely.