639 persons can repair a road in 12 days working 5 hours a day. In how many days will 30 persons working 6 hours a day complete the work ?

$$\eqalign{ & {\text{According to the question,}} \cr & {\text{Let, D is number of days}} \cr & \frac{{639 \times 12 \times 5}}{{1{\text{ road}}}} = \frac{{30 \times 6 \times {\text{D}}}}{{1{\text{ road}}}} \cr & \Leftrightarrow {\text{D}} = {\text{213 days}} \cr} $$