Solution:

Number of blue marbles = 7

Number of white marbles = 8

Number of black marbles = 5

Total number of marbles = 7+8+5 = 20

(i) Probability of getting black ,

= 5/20

= 1/4

Hence the probability of getting black is 1/4.

(ii)Probability of blue or black,

= (7+5)/20

= 12/20

= 3/5

Hence the probability of blue or black is 3/5.