Question

Let A and B be two sets such that n(A) = 5, n(A U B)=9 , n(A∩ B ) = 2 find n(B)

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Answer 1

Answer:

Given, n(A)=5,n(A∪B)=9,n(A∩B)=2

We need to find n(B)

We know n(A∪B)=a(A)+n(B)−n(A∩B)

⇒9=5+n(B)−2

⇒n(B)=6

Answer 2

As we know that,

$\purple{\tt \Longrightarrow n(A\cup B) = n(A)+n(B)-n(A\cap B)}$

${\tt \Longrightarrow 9 =5+n(B)-2}$

${\tt \Longrightarrow 9 - 5 + 2 =n(B)}$

${\tt \Longrightarrow 6 =n(B)}$

Hence 6 is the required answer.