X, Y and Z can complete a piece of work in 8, 20 and 25 days respectively. Working together, they will complete the same work in:
Let the total work be 200 units
Efficiency of X = 200/8 = 25 units per day
Efficiency of Y = 200/20 = 10 units per day
Efficiency of Z = 200/25 = 8 units per day
Total efficiency of X, Y and Z together = 43 units per day.
Therefore, X, Y and Z together can do the work in $$\dfrac{200}{43}$$ days
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