P, Q and R can do a piece of work in 20, 30 and 60 days respectively. In how many days can P do the work if he is assisted by Q and R on every third day?
Choose one
A) 15 days	B) 18 days	C) 20 days	D) 25 days	E) 10 days
P 2 days work = 1/20*2 = 1/10   (P + Q+ R)'s 1 day work ( 1/20 + 1/30 + 1/60) = 6/60 = 1/10   work done in 3 days = 1/5   so 1/5 work done in 3 days   whole work  ( 3* 5)= 
<gadget id="calculator"> ( 3* 5)</gadget>
<output>15</output>
15 days   15 daysNSWER 15 days
<result>A</result>
P, Q and R can do a piece of work in 20, 30 and 60 days respectively. In how many days can P do the work if he is assisted by Q and R on every third day?