- A90 min
- B100 min
- C80 min
- D40 min
Step-by-Step Solution
First 1,000 L at 25 L/min: 40 min. Next 1,000 L at 20 L/min: 50 min. Total 90 min. (100 min has the leak from the start; 80 min ignores it.)
Answer: A) 90 min
A cistern holds 2,000 litres. Its inlet supplies 25 litres per minute; a leak drains 5 litres per minute, but only once the cistern is more than half full. How long does the empty cistern take to fill?
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