Question

Let A be the set of natural numbers which are multiples of 5 strictly less than 100, and B be the set of natural numbers which divide 100. What are the cardinalities of B \ A (the set of elements in B but not in A), A ∩ B and B?

Answer 1

Set A included: 5,10,15,20,25,30,35,40,45,50,55,60,65,70,75,80,85,90,95.

Set B included: 1,2,4,5,10,20,25,50,100

Set A Union Set B included :5,10,20,25,50 (numbers included in both set A and Set B such group is called union group)