Two rectangular containers, P and Q, hold water for a garden watering project. Container P has a base area of 18 cm² and the water in it is 40 cm high. Container Q has water that is 10 cm high. At first, the volume of water in Container P is 2 times the volume of water in Container Q. Some water is then poured from Container P into Container Q until the water level in both containers is at the same height. No water spills out.
- Find the base area of Container Q.
- Find the volume of water poured from Container P into Container Q.
Need a hint?
Find the volume of water in P first. Use it to find the volume in Q, then divide by the height to get the base area.
Worked answer
- (a) Volume of water in P = 18 × 40 = 720 cm³.
- P has 2 times as much water as Q, so volume of water in Q = 720 ÷ 2 = 360 cm³.
- Base area of Q = 360 ÷ 10 = 36 cm².
- (b) Total volume of water = 720 + 360 = 1080 cm³.
- Total base area of P and Q = 18 + 36 = 54 cm². Final height = 1080 ÷ 54 = 20 cm.
- P finally has 18 × 20 = 360 cm³, so the water poured out of P = 720 − 360 = 360 cm³.
The mistake this question tests
Left out the units
Many pupils work out the water poured by using the heights only, such as 40 − 20 = 20, and forget to multiply by the base area to change the height into a volume.
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See the answer →Practise PSLE area & volume until the mistakes stop.
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