Here's a question from a practice test I took:

In a room of 7 people, 4 people have exactly 1 sibling in the room and 3 have exactly 2 siblings in the room. If 2 individuals are selected at random, what is the probability that they are not siblings?
a) 5/21
b) 3/7
c) 4/7
d) 5/7
e) 16/21

The answer is E, but I don't understand why... because if there are 7 people in the room, there should be 2 pairs of siblings (accounting for four of the people), and one set of triplets.

Hi Alyssa,

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