AlgebraMediumWhen a draining tank reaches empty
Algebra practice question
A tank holds 840 liters at noon and drains at a constant rate. At 12:45 p.m. it holds 300 liters. How many minutes after noon will the tank be empty?
Answer: 70
The tank loses 540 liters in 45 minutes, a rate of 12 liters per minute. Emptying 840 liters takes 840 ÷ 12 = 70 minutes.
Common wrong answers
- If you answered 25
- 25 minutes is the time to drain the remaining 300 liters after 12:45 — the question asks for total minutes after noon: 45 + 25 = 70.
- If you answered 45
- At 45 minutes the tank still holds 300 liters; it needs 300 ÷ 12 = 25 more minutes.
- If you answered 63
- Check the rate: 540 liters in 45 minutes is 12 L/min, so empty comes at 840 ÷ 12 = 70 minutes.
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