Given that there are 5 red 4 green and 3 blue balls
The probability of picking a blue and a red ball with replacement is
The probability of picking a blue ball
= 3/(5 + 4 + 3)
= 3/12
The probability of picking a red ball (after replacing the blue picked earlier)
= 5/(5 + 4 + 3)
= 5/12
Hence the probability of picking a blue and a red ball with replacement is
= 3/12 * 5/12
= 15/144
= 5/48