P, Q and R can complete a work in 10 days, 20 days and 30 days, respectively, working alone. How soon can the work be completed if P is assisted by Q and R on alternate days?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 7 1/17 days.
Let the amount of work to be done = 60 units
P's one day work = 6 units
Q's one day work = 3 units
R's one day work = 2 units
If Q and R assist P on alternate days, then the amount of work done in 2 days
= 2 × 6 + 3 + 2 = 17 units
Thus, 60 units will be completed in 2 × (60/17) = 7 × (1/17) days