Advanced MathVery hardTime for repeated halving
Advanced Math practice question
A medicine's concentration in the blood halves every 4 hours. If the concentration is 16 units at noon, at what time will it first be 2 units? Give the answer as the number of hours after noon.
Answer: 12
16 → 8 → 4 → 2 is three halvings, or 12 hours.
Common wrong answers
- If you answered 4
- 4 is one halving.
- If you answered 8
- 8 is two halvings, reaching 4 units.
- If you answered 14
- 14 subtracts 2 from 16 as though the drop were the number of hours.
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