Question

If A={1,3,5,7} and B={1,3,7}. Is set B a proper subset of set A? Explain.

Answer 1

Since for any $b\in B=\{1,3,7\}$ we have that $b\in A=\{1,3,5,7\},$ we conclude that $B$ is a subset of $A.$ Since $5\in A\setminus B,$ we conclude that $B$ a proper subset of set $A.$