A man can do a piece of work in 5 days, but with the help of his son he can do it in 2 days. In what time can the son do it alone ?  Choose the correct option:
A) 7 1/2 days
B) 6 1/2 days
C) 5 1/3 days
D) 3 1/3 days
E) None of these
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 =   (1/2−1/5)=(5−2)/10=3/10   So son will do whole work in 10/3 = 3 1/3 days   Answer: 3 1/3 days
<result>D</result>
A man can do a piece of work in 5 days, but with the help of his son he can do it in 2 days. In what time can the son do it alone ?