Discussion

Explanation:

In 1 hour, the inlet pipe will fill $\frac{1}{8}$ of the tank.

Let the time taken by the outlet pipe to empty the tank be ‘x’ hours. So in 1 hour,
The outlet pipe will empty $\frac{1}{x}$ of the tank in 1 hour.

Together they fill the tank in 10 hours.

⇒ $\frac{1}{8}$ - $\frac{1}{x}$ = $\frac{1}{10}$

∴ x = 40

⇒ Outlet pipe takes 40 hours to empty the full tank.
∴ Outlet pipe will take 20 hours to empty half the tank.

Hence, option (a).

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