Four numbers are selected from the following list of numbers: - 5, - 4, - 3, - 2, -1, 1, 2, 3, 4.
(a) In how many ways can the selections be made so that the product of the four numbers is positive and
(i) The numbers are distinct?
(ii) Each number may be selected as many as four times?
(iii) Each number may be selected at most three times?
(b) Answer part (a) with the product of the four numbers negative.