A and B can do a piece of work in 10 days, B and C in 15 days, C and A in 12 days. How long will C take to do it?	Answers:	A) 70 days	B) 55 days	C) 24 days	D) 40 days	E) 11 days

Rationale: "2 c = 1 / 15 + 1 / 12 – 1 / 10 = 1 / 20 c = 1 / 40 = > 40 days answer : d"
Answer: D