RBI Assistant Prelims 2015 Sitting 1 Paper

Total number of balls in the bag = 7 + 5 = 12
Total possible outcomes Selection of 3 balls out of 12 balls =12C3=

12×11×10

1×2×3

=220
Total favourable outcomes = Selection of 2 balls out of 7 red balls and selection of 1 ball out of 5 green balls =7C2×5C1=

7×6

1×2

×5=105
Required probability

105

220

=

21

44