Question

in a room with 7 people, 4 people have exactly 1 friend in the room and 3 people have exactly 2 friends in the room (assuming that friendship is a mutual relationship, i.e. if jane is paul’s friend, paul is jane’s friend). if two individuals are selected from the room at random, what is the probability that those two individuals are not friends?

Answer 1

$<b><u><i>$Divide 7 people into 2 groups

▶️Group 1 including 4 people have exactly 1 sibling


▶️Group 2 including 3 people have exactly 2 siblings .


First person: 


If he is from G1 (probability: 4/7), the probability that the second one is not his sibling: 5/6 so


=>4/7×5/6=10/21


If he is from G2 (probability: 3/7), the probability that the second one is not his sibling: 4/6 so


=>3/7×4/6=6/21


Now

A/Q

10/21+6/21 = 16/21

ThankS


Have a colossal day ahead


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