arithmetic - yuvraj and dhanraj can do a piece of work in 15 days and 5 days respectively yuvraj started the work alone and then after 5 days dhanraj joined him till the completion of the work how long did the work last - skillgun

Solution: Let A = Yuvraj, B = Dhanraj.
work done by A in 5 days = (5*1/15) = 1/3. remaining work = (1 - 1/3) = 2/3.
(A+B)'s 1 day's work = (1/15 + 1/5) = 4/15.
now, 4/15 work done by A and B in 1 day.
So, 2/3 work will be done by A and B in (15/4 * 2/3) = 2.5 days.
Hence, total time taken = (5+2.5) = 7.5 days.