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

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,
$$\eqalign{ & \Leftrightarrow \frac{5}{8}:\frac{3}{8}::10:x \cr & \Leftrightarrow \frac{5}{8} \times x = \frac{3}{8} \times 10 \cr & \Leftrightarrow x = \left( {\frac{3}{8} \times 10 \times \frac{8}{5}} \right) \cr & \Leftrightarrow x = 6 \cr} $$