State which of the given collections are sets :
(i) collection of all poor people of Dhanbad
(ii) collection of all difficult problem in your maths book
(iii) collection of all fools
(iv) collection of all countries of Asia
(v) collection of four countries of Asia
(vi) collection of three cities of India whose name start with the letter 'J'
(vii) collection of all people in this world over 50 years of age.

Answer

(iv) and (vii) are sets, whereas (i), (ii), (iii),(v) and (vi) are not sets because these collections are not well defined