Which Tank Will Empty First? The Answer Is Easier Than It Looks

At first glance, this puzzle seems almost too simple. Two tanks are sitting side by side, one filled with water and the other with milk. Both have an opening near the bottom, and liquid is flowing out at what appears to be a similar rate.

But there’s a small detail that changes everything.

Which tank will empty first — A or B?

Take a Close Look

Tank A contains water, while tank B contains milk. The containers appear to be the same size, and the liquid levels look almost identical.

That makes it tempting to focus on the type of liquid.

But the real clue is the position of the openings.

The outlet on Tank A is positioned slightly lower than the outlet on Tank B. That means the liquid in Tank A can continue draining until the water level reaches that lower point.

So, Which One Wins?

The answer is A — the water tank.

The important factor isn’t simply whether the tank contains water or milk. It’s the height of the outlet.

As a tank drains, the pressure pushing liquid through the opening decreases as the liquid level falls. A lower outlet allows the tank to drain farther before the flow stops.