Question

In a room filled with 7 people, 4 people have exactly 1 sibling in the room and 3 people have exactly 2 siblings in the room. If two individuals are selected from the room at random, what is the probability that those two individuals are not siblings? 5/21 3/7 4/7 5/7 16/21

Answer 1

Let's divide them into groups of siblings..
Group - 1 : A,B
Group -2 : C,D
Group - 3 : E,F,G

A,B,C,D have only one sibling and E,F,G have 2 siblings.

rest are written in the picture..