Question

There are 7 people in a room . 4 have exactly 3 siblings while 3 have exactly 1 sibling. If 2 of the 7 are chosen , find the probability that they are not siblings .

Answer 1

Question is wrong one..this condition is not possible for the question.
You have changed question .I will send the real question.
question is 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

Selection of 2 out of 7 people=7c2=21

As per question 1-2 , 3-4 are those 4 people with one sibling and 5-6-7 are people with 2 siblings.

Now finding selection of 2 siblings==

=(2c2+2c2+3c2)÷(7c2)=(1+1+3)÷21

=(5÷21)

But we need selection of 2 those who are not siblings.

So probability of negative=1-probability of positive
=1-(5÷21)=(21-5)÷21=(16÷21)

it is the answer.

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