arithmetic - purnima does half as much work as rohini and neelima does half as much work as purnima and rohini together if neelima alone can finish the work in 40 days then together all will finish the work in - skillgun

Let A = Purnima, B = Rohini, C = Neelima.
C alone can finish the work in 40 days.
(A + B)can do it in 20 days
(A + B)s 1 days wok = 1/20.
As 1 days work : B's 1 days Work = 1/2 : 1 = 1:2.
A’s 1 day’s work = (1/20) * (1/3) = (1/60). [Divide 1/20 in the ratio 1:2]
B's 1 days work = (1/20) * (2/3) = 1/30
(A+B+C)'s 1 day’s work = (1/60) + (1/30) + (1/40) = 9/120 = 3/40
All the three together will finish it in 40/3 = 13 and 1/3 days.