A man can do a piece of work in 6 days, but with the help of his son he can do it in 3 days. In what time can the son do it alone ?  Options.
A) 7 days B) 6 days C) 5 days D) 4 days E) none of these

Rationale: "explanation : in this type of question , where we have one person work and together work done . then we can easily get the other person work just by subtracting them . as son ' s one day work = ( 1 / 3 − 1 / 6 ) = ( 6 − 3 ) / 18 = 1 / 6 so son will do whole work in 6 days answer : b"
Answer: B