4) C
Total number of balls = (x + y + z)
Probability of first ball being red = x
x + y + z
Since the ball is replace, the total number of balls will remain the same, i.e., (x + y + z)
Probability of second ball being blue = y
x + y + z
Probability of first ball being red and second ball being blue:
x x y
x + y + z x + y + z
xy
(x + y + z)²
