5 men can paint a hall in 18 hours. How many men will be able to paint it in 10 hours?

Men required to paint in 18 hours = 5 men.

Men required to paint in 1 hour = (5 x 18) men. $\quad$ [Less time, More men]

Men required to paint in 10 hours = $\Big(\dfrac{5 \times 18}{10}\Big) \text{ men} \quad \text{[More time, Less men]}$

= $\dfrac{90}{10}$ men

= 9 men.

9 men are required to paint in 10 hours.