Multiple choice general knowledge math & puzzles

In the middle of a round pool lies a beautiful water-lily. The water-lily doubles in size every day. After exactly 20 days the complete pool will be covered by the lily. After how many days will half of the pool be covered by the water-lily?

  1. 12 days

  2. 16 days

  3. 10 days

  4. 19 days

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Since the lily doubles in size every day, if it covers the whole pool on day 20, it must have covered exactly half of the pool on the previous day (day 19).