AlgebraEasy–MediumFewest whole units to exceed a threshold
Algebra practice question
A tank holds 75 litres of fuel. A generator uses 9 litres per hour. After how many whole hours of running will the tank hold less than 10 litres?
Answer: 8
75 − 9h < 10 gives 9h > 65, h > 7.2. The first whole hour is 8. (After 8 hours: 75 − 72 = 3 litres.)
Common wrong answers
- If you answered 7
- After 7 hours, 12 litres remain — not yet under 10.
- If you answered 9
- 9 is later than needed; 8 hours already leaves 3 litres.
- If you answered 7.2
- 7.2 is the exact threshold, but the question asks for whole hours.
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