A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days A do the work if he is assisted by B and C on every third day? Choose the correct choice:
A) 22 days
B) 15 days
C) 77 days
D) 99 days
E) 11 days
A's 2 day's work = (1/20 * 2) = 1/10   (A + B + C)'s 1 day work = (1/20 + 1/30 + 1/60) = 1/10   Work done in 3 days = (1/10 + 1/10) = 1/5   Now, 1/5 work is done in 3 days.   Whole work will be done in (3 * 5)= 
<gadget id="calculator">(3 * 5)</gadget>
<output>15</output>
15 days.   Answer: 15 days
<result>B</result>
A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days A do the work if he is assisted by B and C on every third day?