Question

I need an explanation in words of the answers for the following examples if someone can please:

Are the following a proper subset of A={1,2,3,4,5}?

B={1,3}

C={a,1}

D={}

Answer 1

Given a set A, another set X is a subset of A if every element of X is also an element of A.

So, B is a subset of A, because 1 and 3 both belong to A as well.

C is not a subset of A, because the element 'a' doesn't belong to A

D is a subset of A, because the empty set is a subset of every set.