The idea in brief. Pouring does not change the water. What changes is the floor it is standing on, and the level is the volume of water over the area of that floor. So the same water on a wider floor stands lower, and the arithmetic that says so is a division whose units cancel: cubic centimetres over square centimetres leaves centimetres. In the lesson. A lower level.
Lesson video, with the working
Finding water level from volume and base area
2 min 49 s
The film teaches 1 question. The question shows first; its working is written as the film explains it.
Tanks A and B are rectangular. Tank A is 25 cm long, 16 cm wide and 20 cm high. The water in Tank A is 12 cm deep. Tank B is 40 cm long and 15 cm wide, and it is empty. All the water in Tank A is poured into Tank B. Find the height of the water level in Tank B.
Water level in B = 4800 cm³ ÷ 600 cm² = 8 cm
Ans: 8 cm
How to solve it
Pouring does not change the water. A wider floor means a lower level.
Find Tank A's base area: 25 times 16 is 400 square centimetres.
Find the water's volume using its depth of 12 centimetres, not the tank's height: 400 times 12 is four thousand, eight hundred.
Find Tank B's base area: 40 times 15 is 600 square centimetres.
Divide the volume by Tank B's base area: four thousand, eight hundred divided by 600 is 8 centimetres deep.
Same water. A wider floor. A lower level.
Practice questions with worked solutions
Question 1 is free to try. The other 8 open in the free trial, each with its full working.
How do you solve water level in a tank questions in P6?
The height of water in a rectangular tank is its volume divided by the base area.
What your child learns here
The height of water in a rectangular tank is its volume divided by the base area. This page uses that to find levels, rises and drops, and how much water moved. It applies the Primary 6 outcome on finding a height from a volume and a base area.
Find the water level as the volume of water divided by the base area of the tank.
Use the water's depth, not the tank's height, when finding the volume of water.
Find the water that left a tank as its base area times the drop in level.
Read a fraction full as that fraction of the tank's height.
Add a rise to the level that was already there when the tank was not empty.
Does the answer make sense?
The water's depth can never be more than the tank's height, and water poured into a tank that already holds some must stand higher than before. When water is drawn off or poured out, the level your child finds must be lower than at the start.
How to practise these questions
The Basic questions train the water level as volume divided by base area. Intermediate questions add tanks that are not empty, wider bases, and converting litres to cubic centimetres along the way. Challenge questions treat the air above the water as a box, or pass the water through a chain of tanks whose base areas shrink each time. When the water level stalls, read the written step-by-step solution together.
Questions parents ask
How do you find the height of water in a tank? Divide the volume of water by the base area of the tank. Convert litres to cubic centimetres first, so the answer comes out in centimetres.
How do you find how much water was poured out of a tank? Find the drop in level, the height before minus the height after, and multiply it by the base area.
Is water level in the P6 syllabus? Yes. Finding the height of a cuboid given its volume and base area is a Primary 6 outcome, and the volume of liquid in a rectangular tank is a Primary 5 outcome that it builds on.
