A man can do a piece of work in 5days, but with the help of his son, he can do it in 3 days. In what time can the son do it alone?	Pick one.
A) 13 / 2  B) 7  C) 15 / 2  D) 8  E) 9

Rationale: "son ' s 1 day ' s work = ( 1 / 3 ) - ( 1 / 5 ) = 2 / 5 the son alone can do the work in 15 / 2 days answer is c"
Answer: C