A) 15 days
B) 10 days
C) \[7\frac{1}{2}\text{days}\]
D) 5 days
Correct Answer: A
Solution :
The ratio of efficiency of X and Y to do the work 3E : E \[\therefore \]Time taken to do the work by X and Y= E : 3E Then, \[3E-E=40\] \[\Rightarrow \] \[2E=40\] \[\Rightarrow \] \[E=20\]days \[\therefore \](X + Y)'s one day work \[=\frac{1}{20}+\frac{1}{60}=\frac{3+1}{60}=\frac{4}{60}\] \[=\frac{1}{15}\] Hence, X and Y together complete the work in 15 days.
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