Let the leak empties the full tank in x h then

Part emptied in 1 h by leak = \( \Large \frac{1}{x} \)

Part filled by inlet in 1 h = \( \Large \frac{1}{20} \)

According to the question.

\( \Large \frac{1}{20} \)+\( \Large \frac{1}{x} \)=\( \Large \frac{1}{40} \)

Therefore, \( \Large \frac{1}{x} \) = \( \Large \frac{1}{40} \)-\( \Large \frac{1}{20} \)

= \( \Large \frac{1-2}{40} \)= \( \Large - \frac{1}{40} \)

[Negative sign indicates emptying]

Clearly, leak will empty the full tank in 40 h