A) 3 days
B) 5 days
C) 10 days
D) 12 days
E) 15 days
Correct Answer: A
$ \therefore $ In 1 day, they can complete $ =\frac{3}{20}part $
$ \therefore $ In 5 day, then can complete $ =5\times \frac{3}{20}=\frac{3}{4}part $ Remaining work $ =1-\frac{3}{4}=\frac{1}{4} $ Time taken by A to complete the work $ =\frac{\frac{1}{4}}{\frac{1}{12}}=3days $