AlgebraHardTime to reach zero from two readings
Algebra practice question
A water butt held 80 litres at 6 a.m. and 50 litres at noon, draining at a constant rate. At what time will it be empty?
- A. 10 p.m.Correct
- B. 6 p.m.
- C. midnight
- D. 4 p.m.
Answer: A. 10 p.m.
30 litres in 6 hours is 5 litres per hour. From 80 litres at 6 a.m., emptying takes 16 hours: 10 p.m.
Why the other answers are wrong
- B. 6 p.m.
- 6 p.m. is 12 hours on, when 20 litres remain.
- C. midnight
- Midnight is 18 hours on, past empty.
- D. 4 p.m.
- 4 p.m. is 10 hours on, when 30 litres remain.
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