A man can do a piece of work in 15 days, but with the help of his son, he can do it in 6 days. In what time can the son do it alone?	Choose one:
A) 13	B) 9	C) 15	D) 8	E) 10

Rationale: "son ' s 1 day ' s work = ( 1 / 6 ) - ( 1 / 15 ) = 3 / 30 = 1 / 10 the son alone can do the work in 10 days answer is e"
Answer: E