A, 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?
Choose the correct answer:
A) 12	B) 13	C) 15	D) 16	E) 18
2 day work = 1/20*2=1/10   A+B+15 1 day work = 1/10   work done in 3 days = 1/5   1/5 work is done in 3 days   whole work will done in   (3*5)= 
<gadget id="calculator">  (3*5)</gadget>
<output>15</output>
15 days
<result>C</result>
A, 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?