A man can do a piece of work in 4 days, but with the help of his son he can do it in 3 days. In what time can the son do it alone ?	Select the correct option:
A) 12 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 / 4 ) = ( 4 − 3 ) / 12 = 1 / 12 so son will do whole work in 12 days answer : a"
Answer: A