A roof of area 3 sq m receives 30 mm rainfall in one day. If 70% of this rainwater can be collected in a bucket, how many litres of water are collected in one day?
Answer
63 litres
The correct answer is 63 litres — 3. Apply collection efficiency: 70 % of 90 litres = 0.7 × 90 = 63 litres.
Step-by-step solution
- 1. Convert rainfall depth to litres per square metre. 1 mm of rain on 1 sq m = 1 litre, so 30 mm = 30 litres/sq m.
- 2. Calculate total volume on the roof: 30 litres/sq m × 3 sq m = 90 litres.
- 3. Apply collection efficiency: 70 % of 90 litres = 0.7 × 90 = 63 litres.
Common mistake: Not converting mm to litres per square metre or forgetting to apply efficiency
Concept tested: Water collection from rainfall
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