In how many ways can 4 red, 3 yellow and 2 green discs be arranged in a row, if the discs of the same colour are indistinguishable?

Step-by-step solution

Total number of dises are 4+3+2=9 . Out of 9 dises, 4 are of the first kind (red) 3 are of the second kind (yellow) and 2 are of the third kind (green). Therefore, the number of arrangements = 9 ! 4 ! 3 ! 2 ! =1260