Total number of beads = 3 + 8 + 7 = 18. P(red) = total number of red/total number of beads = 3/18 = 1/6. P(blue) = total number of blue beads/total number of beads left after replacement = 8/17. P(black) = total number of black beads/total number of beads left after replacement = 7/16. Therefore P(red) = 1/6. P(blue) = 8/17. P(black) = 7/16.