Picking Friends - Combinotorics Problem

[niaz.nm]

Hi,
Can you please explain the below problem in detail to me?

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?

a) 5/21
b) 3/7
c) 4/7
d) 5/7
e) 16/21

[george.kourdin]

siblings-problem-combinatorics-t9048.html

[niaz.nm]

Thanks george.. That was really helpful...

[jnelson0612]

Thanks George!