A man can do a job in 10 days. His father takes 20 days and his son finishes it in 25 days. How long will they take to complete the job if they all work together? Choose the correct answer:
A) 6.3  B) 6.9  C) 5.3  D) 6.1  E) 6.2
1 day work of the three persons = (1/10 + 1/20 + 1/25) = 19/100   So, all three together will complete the work in 100/19 = 5.3 days.   Answer:5.3
<result>C</result>
A man can do a job in 10 days. His father takes 20 days and his son finishes it in 25 days. How long will they take to complete the job if they all work together?