AlgebraHardTime for a battery to reach a level
Algebra practice question
A phone's battery drops from 100% to 40% in 5 hours, losing charge at a constant rate. At this rate, how many hours after starting at 100% will the battery reach 16%?
Answer: 7
The rate is (100 − 40)/5 = 12 percentage points per hour. To fall from 100 to 16 is 84 points: 84/12 = 7 hours.
Common wrong answers
- If you answered 2
- 2 is the time from 40% to 16% (24/12). The question asks for the time from 100%.
- If you answered 6
- 6 comes from an incorrect rate of 14 points per hour; the rate is 60/5 = 12.
- If you answered 8.33
- 8.33 is 100/12, the time to reach 0%, not 16%.
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