AlgebraMediumTime for a linearly draining quantity to reach a level
Algebra practice question
A phone's battery drains at a constant rate, from 100% at 8 a.m. to 40% at 2 p.m. How many hours after 8 a.m. will the battery reach 10%?
Answer: 9
It loses 60% in 6 hours, so 10% per hour. From 100% to 10% is 90%, which takes 9 hours.
Common wrong answers
- If you answered 3
- 3 is the time from 40% to 10%, not from 8 a.m.
- If you answered 6
- 6 hours brings it to 40%, not 10%.
- If you answered 10
- 10 hours brings it to 0%.
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