So the (effective) fraction of work performed each day = A's share +1/3 B&C share =1/20 +(1/30/1/60)/3 = 1/15A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?
why it is 1/30/1/60? i mean B+C or B*C??