A can do a piece of work 20 days. B can do work in 35 days. In how many days they will complete the work together?	Options.
A) 15 days	B) 16.32 days	C) 12.72 days	D) 17 days	E) 18 days

Rationale: "lcm = 140 , ratio = 20 : 35 = 4 : 7 no of days = 140 / ( 4 + 7 ) = 90 / 5 = 12.72 days answer : c"
Answer: C