A service-station storage tank needs refilling as there are only 1500 litres left in the tank. Petrol is pumped into the tank at the rate of 750 litres per minute.How much petrol is in the tank at the start of the third minute? (write the value only, units not required)

Question

BlackTom AI · Accepted Answer

Since petrol is added at a constant rate of 750 litres per minute, the amount in the tank increases linearly by 750 L each minute.

1. Relevant knowledge points and concepts
- Constant rate problems: when a quantity is increasing at a fixed rate, total change = rate × time.
- “Start of the nth minute” means after (n − 1) full minutes have elapsed. So the start of the third minute is after 2 full minutes of pumping.

2. Step-by-step reasoning
- Initial amount at time 0 (start of the first minute): 1500 L.
- After 1 minute (start of the second minute): add 750 L.
- After 2 minutes (start of the third minute): add another 750 L.

3. Intermediate calculations
- After 1 minute: 1500 + 750 = 2250 litres.
- After 2 minutes: 2250 + 750 = 3000 litres.
Alternatively using rate × time: additional petrol after 2 minutes = 750 × 2 = 1500 litres. Total = initial 1500 + 1500 = 3000 litres.

4. Why the correct answer is correct
- The calculation directly applies the constant rate over the two full minutes that pass before the start of the third minute, giving a total of 3000 L.

5. Why other plausible answers would be incorrect
- 2250 would be the amount at the start of the second minute (after 1 minute), not the third.
- 3750 would be the amount after 3 full minutes (start of the fourth minute), not the third.
- Any answer not equal to 3000 fails to account for the two full minutes of pumping before the third minute begins.

6. Conclusion
The amount of petrol in the tank at the start of the third minute is 3000, which matches the provided answer.

A service-station storage tank needs refilling as there are only 1500 litres left in the tank. Petrol is pumped into the tank at the rate of 750 litres per minute.How much petrol is in the tank at the start of the third minute? (write the value only, units not required)Short answer

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