Question : X and Y together can do a piece of work in 30 days. Z alone can do it in 60 days. If they worked together, then in how many days they can finish the work?
Option 1: 50
Option 2: 25
Option 3: 45
Option 4: 20
Correct Answer: 20
Solution :
X and Y together can do a piece of work in 30 days.
⇒ 1 day's work of X + Y = $\frac{1}{30}$
Z alone can do it in 60 days.
⇒ 1 day's work of Z = $\frac{1}{60}$
So, 1 day's work of X + Y + Z = $\frac{1}{30}+\frac{1}{60}=\frac{1}{20}$
Therefore they will finish the work in 20 days working together.
Hence, the correct answer is 20.
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