##### Set Theory Basics(1)

**Subset**: B is called a subset of A if the number of elements in B is less than or equal to A. Ex:

A ={1,2,3,4}

B={2,3,4}

We can say that B ⊆ A

**Proper Subset:**

B is called the proper subset of A if A contains at least one element that B doesn't contain. So A is also called as a proper superset. B⊂ A.

**The cardinality of the set**: Number of elements present in a set is called the cardinality of the set. Ex:

X={a,b,c,d,e,f,g}

Cardinality is denoted of X is written as |X|

|X| = 7

Null Set: A set having no element is called a null set. It is denoted by {} or Ø

But {Ø} is not a null set.

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