P, Q and R can do a work in 20, 30 and 60 days respectively. How many days does it need to complete the work if P does the work and he is assisted by Q and R on every third day?	Choose one.
A) 15 B) 24 C) 78 D) 96 E) 32
Explanation :   15mount of work P can do in 1 day = 1/20   15mount of work Q can do in 1 day = 1/30   15mount of work R can do in 1 day = 1/60   P is working alone and every third day Q and R is helping him   Work completed in every three days = 2 × (1/20) + (1/20 + 1/30 + 1/60) = 1/5   So work completed in 15 days = 5 × 1/5 = 1   Ie, the work will be done in 15 days   15NSWER:15
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P, Q and R can do a work in 20, 30 and 60 days respectively. How many days does it need to complete the work if P does the work and he is assisted by Q and R on every third day?