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Universal set is the set containing all objects or elements and of which all other sets are subsets. Universal set is denoted by 'U'.

Example-

A= {x:x is a student of Class 5 A}

B= {x:x is a student of Class 5 B}

C= {x:x is a student of Class 5 C}

U= {x:x is a student of Class 5}

In mathematical terms we can say that A is a proper subset of U i.e A⊂U, for A to be a proper subset of U there has to be atleast one element in U that is not present in A.

Similarly, B⊂U and C⊂U.