A man can do a job in 15 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?
A). Less than 6 days
B). Exactly 6 days
C). Approximately 6.4 days
D). More than 10 days
Approximately 6.4 days
1 day work of the three persons = (1/15 + 1/20 + 1/25) = 47/300
So, all three together will complete the work in 300/47 = 6.4 days.
8. If 12 men do a work in 80 days, in how many days will 16 men do it?