A man can do a job in 5 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?  Choices: A) 6.3 B) 6.9 C) 3.5 D) 6.1 E) 6.2
1 day work of the three persons = (1/5 + 1/20 + 1/25) = 29/100   So, all three together will complete the work in 100/29 = 3.5 days.   Answer:3.5
<result>C</result>
A man can do a job in 5 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?