A man can do a piece of work in 10days, but with the help of his son, he can do it in 4 days. In what time can the son do it alone?  Pick.
A) 13/2	B) 17/3	C) 15/2	D) 20/3	E) 9
Son's 1day's work = (1/4)-(1/10) = 3/20   The son alone can do the work in 20/3 days   Answer is 20/3
<result>D</result>
A man can do a piece of work in 10days, but with the help of his son, he can do it in 4 days. In what time can the son do it alone?