A can do a piece of work 60 days. B can do work in 20 days. In how many days they will complete the work together?  Select
A) 12 days	B) 16 days	C) 15 days	D) 17 days	E) 18 days

Rationale: "lcm = 60 , ratio = 60 : 20 = 3 : 1 no of days = 60 / ( 3 + 1 ) = 90 / 4 = 15 days answer : c"
Answer: C