**If π΄ and B are finite sets which are subsets of π. Establish a formula for π(π΄ βͺ π΅) in terms of π(π΄), π(π΅) and π(π΄ β© π΅). Hence or otherwise deduce a formula for a particular case where A and B are disjoint?**

The **Answer to the Question**

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**Here's the Solution to this Question**

We have that

$n(A\cup B)=n(A)+n(B)-n(A\cap B)$

because if we writeΒ $n(A)+n(B)$Β we are counting each element ofΒ $A\cap B$Β twice.

$A$Β andΒ $B$Β are disjoint if they have no elements in common. That is,Β $n(A\cap B)=0$Β . Therefore, substituting to the above formula we deduce that

$n(A\cup B)=n(A)+n(B).$