The collection of all natural numbers less than 10,000 forms a set.
Which of the following collections are sets ? Justify your answer :
(i) A collection of all natural numbers less than 50.
(ii) The collection of good hockey players in India.
(iii) The collection of all girls in your class.
If U= set of all whole numbers less than 12, A=set of all whole numbers less than 10, B= Set of all odd natural numbers less than 10, then what is (A ∩ B)'?