Multiple choice general knowledge math & puzzles

In a pot there are some bacteria. And in every half day the volume of bacteria doubles and in 10 days the pot becomes full. Then in how many days the pot will become exactly half?

  1. 4.5

  2. 5

  3. 5.5

  4. 8.5

  5. 9.5

  6. 9
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Since bacteria double every half day, working backwards from day 10 (full), the pot was half-full exactly one half-day earlier. On day 9.5, the pot was half full, then doubled to become full on day 10. This is a classic exponential growth puzzle.

AI explanation

Bacterial volume doubles every half day (12 hours), so it's growing exponentially. Working backwards from a full pot at 10 days, the volume was exactly half of full one doubling-period earlier — that is, half a day (12 hours) before the pot became completely full. So the pot reaches exactly half-full at 10 - 0.5 = 9.5 days. This is the classic "doubling" trick question: since each step doubles the volume, the second-to-last step must be exactly half, not some earlier fractional calculation. All other options (4.5, 5, 5.5, 8.5, 9) don't correspond to exactly one halving-period before full capacity. 9.5 is correct.

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