(a) It means that you chose all 3 yam tubers from the set of 15-5 = 10 yam tubers that are not spoilt.
Therefore, the probability (a) is P = = = = = 0.2637. ANSWER
(b) It means that you chose all 3 yam tubers from the set of 5 yam tubers that are spoilt.
Therefore, the probability (b) is P = = = = = 0.0220. ANSWER
(c) In this case, the probability is P = = = 0.4945. ANSWER
(d) In this case, the probability is the COMPLEMENT to case (a) P = 1 - 0.2637 = 0.7363. ANSWER