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How deep will the water be?

A hard-level "Length" problem.Levelling problems are always "all the water ÷ total base area". However many tanks there are, join them into one and nothing changes.

GivenTank A (base 20 × 10 cm) holds water 12 cm deep. Pour into the empty tank B (base 10 × 10 cm) until both are equally deep

Length ★★★★☆☆ How deep will the water be? A B 12cm 20cm 10cm

Hints

  1. Pouring does not change how much water there is. Start by measuring what A holds: 20 × 10 × 12 = 2400 cm³.
  2. Picture the finished state. Since both depths are equal, you may treat the surface as one single flat level across both tanks.
  3. Which means you may treat the two tanks as one big tank. Its base area is 200 + 100 = 300 cm².
  4. Depth is "volume ÷ base area": 2400 ÷ 300

Answer 8cm

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