Q4. A fish tank measures 30cm wide by 40cm high by 70cm long.
It is filled with water to 3⁄4 of its height.
Purifier is used at the rate of 1 tablet for every 2 litres. How much extra purifier would be needed if the tank was filled to the top?
(2 marks)
Answer and commentary The first complication here is the mix of units. The tank is measured in centimetres, but the purifier details are given in litres.
So, it is important to know that 1 litre fills 1000cm3.
Now, the tank is currently 3⁄4 full. The height of the tank is 40cm, so 3⁄4 of 40cm is 30cm.
That means we have 10cm left to fill.
The base of the tank is 30cm x 70cm. So the volume left to fill is:
30 x 70 x 10 = 21000cm3.
That is 21 litres.
We need 1 tablet for every 2 litres, so we will need 11 tablets (not 10 because that wouldn't be enough).
Answer: 11 tablets Next question
 | 
