arithmetic - harish and peter working separately can paint a building in 18 days and 24 days respectively if they work for a day alternately harish beginning in how many days the painting work will be completed - skillgun

Solution: Let A = Harish, B = Peter.
(A+B)'s 2 day's work =(1/18 + 1/24) = 7/72.
work done in 10 pairs of days = (10*7/72) = 70/72.
remaining work = (1 - 70/72) = 2/72 = 1/36.
on 21st day, it is A's turn. 1/18 work is done by him in 1 days.
1/36 work id done by him in (18*1/36) = 1/2 day.
.'. total time taken = (20+1/2) days = 20 1/2 days.