Advanced MathHardStarting value of a tripling quantity
Advanced Math practice question
A quantity triples every hour. Two hours after the start, the quantity is 18. What was the quantity at the start?
Answer: 2
Two triplings multiply the start by 9: 9 × start = 18, so the start was 2.
Common wrong answers
- If you answered 3
- 3 is the growth factor, not the starting value.
- If you answered 6
- 6 undoes only ONE tripling (18/3); two hours means two triplings.
- If you answered 12
- 12 is 18 − 6, subtracting instead of dividing.
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