A) 5 days
B) 6 days
C) 7 days
D) 8 days
Correct Answer: D
$ \therefore $ Ratio of work $ =\frac{1}{5}:\frac{1}{4}:\frac{1}{2}=4:5:10 $
$ \Rightarrow $ $ 4M=5W=10C $
$ \Rightarrow $ $ 2M+3W+4C=5C+6C+4C=15C $ and $ 6M+4W+7C=15C+8W+7W=30C $
$ \therefore $ $ x=\frac{15\times 16}{30\times 10}\times 10=8days $