Question
In how many ways can 4 red, 3 yellow and 2 green balls be arranged in a row if the balls of the same colour is indistinguishable?
Solution
Total number of balls = 
n = 9
Number of red balls = 4
p = 4
Number of yellow balls = 3
q = 3
Number of green balls = 2
r = 2
∴ The number of permutations of balls:
= 9 x 4 x 7 x 5 = 1260.
