A can finish a work in 10 days and B can do same work in half the time taken by A. then working together, what part of same work they can finish in a day?  Answers:
A) 1 / 5 B) 1 / 6 C) 1 / 7 D) 3 / 10 E) none of these

Rationale: "explanation : please note in this question , we need to answer part of work for a day rather than complete work . it was worth mentioning here because many do mistake at this point in hurry to solve the question so lets solve now , a ' s 1 day work = 1 / 10 b ' s 1 day work = 1 / 5 [ because b take half the time than a ] ( a + b ) ' s one day work = ( 1 / 10 + 1 / 5 ) = 3 / 10 so in one day 3 / 10 work will be done answer : d"
Answer: D