Hello, fleurdel!

18. There are two tanks filled with water.

They are being emptied by two different taps, each with a constant flow of water.

Tank A is 5 cm taller than Tank B.

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The tap of Tank A was opened at 7:00 a.m.

Tank A was empty at 1:00 p.m.

The tap of Tank B was opened at 8:30 a.m.

Tank B was empty at 12:30 p.m.

The water level of both tanks were equal at 11 a.m.

What is the height of tank A?

. .

. .

. . .[1]

. . .[2]

Substitute [1] into [2]: . .[3]

At ll:00 a.m. the two tanks had the same height.

Tank A: in 4 hours, the level dropped

. . The height was: .

Tank B: in 2.5 hours, the level dropped

. . The height was: .

We have: . .[4]

Solve [3] and [4]: .

Substitute into [1]: .

Therefore, Tank A is 45 cm high.