A bag contains three red marbles, six blue marbles, and three yellow marbles.
therefore total no. of marbles = 3 + 6 + 3 = 12
total no. of red marble = 3
therefore probablity of selecting one red marble is 3/12 = 1/4
again total no. of blue marbles is 6
therefore probability of selecting one blue marble is 6/12 = 1/2
now total probability of selecting one red ball replacing it then selecting one blue marble is. 1/4 * 1/2 = 1/8
