M, N and O can do a piece of work in 60, 30 and 20 days respectively. Inhow many days can M do the work if he is assisted by N and O on every third day? Choose the correct option.
A) 10 days  B) 12 days  C) 15 days  D) 25 days  E) 30 days
M's 2 day's work = 1	x 2 =	1	.   20	10   (M + N + O)'s 1 day's work = 1	+	1	+	1 =	6	=	1	.   20	30	60	60	10   Work done in 3 days = 1	+	1 =	1	.   10	10	5   Now,	1	work is done in 3 days.   5   Whole work will be done in (3 x 5) = 15 days.   15 days
<result>C</result>
M, N and O can do a piece of work in 60, 30 and 20 days respectively. Inhow many days can M do the work if he is assisted by N and O on every third day?