A man completes 5/8 of a job in 10 days. At this rate, how many more days will it take him to finish the job ?

Answer: Option B

Work done = $$\frac{5}{8}$$
Balance work $$=\left(1-\frac{5}{8}\right)$$   $$=\frac{3}{8}$$
Less work, Less days ( Direct proportion)
Let the required number of days be x
Then,
$$\begin{array}{rl}& \iff \frac{5}{8}:\frac{3}{8}::10:x\\ & \iff \frac{5}{8}\times x=\frac{3}{8}\times 10\\ & \iff x=\left(\frac{3}{8}\times 10\times \frac{8}{5}\right)\\ & \iff x=6\end{array}$$