STATISTICS
posted by MIA on .
From a group of 12 people, you randomly select 3 of them. Find the probability that at least one of them is among the 3 oldest people in the group

Hint: It's the complement of the probability that none of them is among that group.
Let En be the indexed event that the nth person selected is not one of the three oldest.
1  P(E1) P(E2E1) P(E3E1 and E2)
= 1  (9/12) (8/11) (7/10)
= 0.61818....