UPSC NDA Math Model Paper 10

The total letters in box III = 3 + 1 + 2 + 5 + 3 + 4 = 18
Out of which:
White letters = 3 + 5 = 8
Blue letters = 1 + 3 = 4
Yellow letters = 2 + 4 = 6
Ways of selecting 2 letters out of 18 without replacement =‌18C2
Ways of selecting 2 letters out of 10 not white letters without replacement =‌10C2
Possibility of the letters picked are not white =

‌10C2

‌18C2

=

10

17