IBPS RRBs Officer Scale I 02 Sep 2012 Paper

(1)
Total possible outcomes n (S)
= Selection of 4 caps out of 12 caps
=

12

‌

C4=

12×11×10×9

1×2×3×4

=495
Favourable outcomes n(E) =Selection of 4 caps out of 7 caps (excluding green caps)
=

7

‌

C4=

7×6×5×4

1×2×3×4

=35
⇒Required probability

n(E)

n(S)

=

35

495

=

7

99