arithmetic - p q and r can do a piece of work in 40 60 and 120 days respectively in how many days can p do the work if he assisted by q and r on every 9th day - skillgun

Solution: A's 8 day's work = (8 *1/40) = 1/5.
(A+B+C)'s 1 day's work = (1/40 + 1/60 + 1/120) = 6/120 = 1/20.
work done in 9 days = (1/20 + 1/5) = (1+ 4)/20 = 5/20 = 1/4.
now, 1/4 work is done in 9 days.
.'. whole work will be done in (9*4) = 36 days.