A pond of volume 500 m³ has dissolved oxygen concentration 8 mg/L. A heatwave causes a 25% drop in dissolved oxygen. Calculate the remaining amount of oxygen in the pond in kilograms.
Answer
3 kg
The correct answer is 3 kg — Apply 25% reduction: 4 kg × 0.75 = 3 kg, which is the remaining oxygen.
Step-by-step solution
- Convert volume to liters: 500 m³ × 1000 L/m³ = 500,000 L.
- Compute initial oxygen: 8 mg/L × 500,000 L = 4,000,000 mg.
- Convert mg to kg: 4,000,000 mg ÷ 1,000,000 mg/kg = 4 kg.
- Apply 25% reduction: 4 kg × 0.75 = 3 kg, which is the remaining oxygen.
Common mistake: missing unit conversions between liters, mg, and kg
Concept tested: dissolved oxygen calculation
Published · How this solution was prepared and checked
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