in a room with 10 people , 6 people have exactly 1 friend in the room and 5 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 ?
( 6 / 10 ) ( 7 / 9 ) + ( 5 / 10 ) ( 6 / 9 ) if you choose one of the 6 with one other friend , then you have a 7 / 9 chance of not picking their friend 2 nd . if you choose one of the 5 with 2 friends , you have a 6 / 9 chance of not picking one of their friends second . add them up . 42 / 90 + 30 / 90 72 / 90 = 4 / 5 c . 4 / 5
divide(subtract(subtract(subtract(10, 1), 1), 1), subtract(10, 1))