X does a work in 30 days. Y does the same work in 45 days. In how many days they together will do the same work?  Choose the correct option.
A) 18 B) 12 C) 20 D) 30 E) 15

Rationale: "x ' s 1 day ' s work = 1 / 30 y ' s 1 day ' s work = 1 / 45 ( x + y ) ' s 1 day ' s work = ( 1 / 30 + 1 / 45 ) = 1 / 18 both together will finish the work in 18 days . correct option is a"
Answer: A