X does a work in 10 days. Y does the same work in 15 days. In how many days they together will do the same work?	Pick one
A) 10  B) 15  C) 3  D) 6  E) 12

Rationale: "x ' s 1 day ' s work = 1 / 10 y ' s 1 day ' s work = 1 / 15 ( x + y ) ' s 1 day ' s work = ( 1 / 10 + 1 / 15 ) = 1 / 6 both together will finish the work in 6 days . correct option is d"
Answer: D