There are 5 balls in the bag so the probability of drawing a green ball first is ⅗. If the ball is not placed back in the bag immediately, there will be 4 balls left in the bag, 2 of which are green. If the second ball is now drawn, the probability of drawing a green is 2/4=½. Therefore the probability of drawing two green balls is ⅗×½=3/10 or 0.3 or 30%.
If the first ball drawn had been placed back in the bag before the second ball had been drawn the probability would have been ⅗2=9/25=0.36 or 36%.