Illustration 4  
        A bag contains 5 red balls, 8 white balls, 4 green balls and 7 black balls. If one ball is drawn at random, find the probability that it is :
        (i) Black    (ii) Not red    (iii) Green
    Solution
        Number of red balls in the bag = 5 
        Number of white balls in the bag = 8 
        Number of green balls in the bag = 4
        Number of black balls in the bag = 7 
        ∴     Total number of balls in the bag = 5 + 8 + 4 + 7 = 24. 
        Drawing balls randomly are equally likely outcomes. 
        ∴    Total number of possible outcomes = 24
        Now, 
        (i)     There are 7 black balls, hence the number of such favourable outcomes = 7