One to think about...
A Scientist has developed a fast growing water lily.
This lily will double it's size every day.
So the Scientist puts the lily in a pond.
The next day there are two of the. The following day it doubles itself and there are 4.
This goes on until on the 20th day the pond is covered.
The question is...On what day is the pond only 1/2 covered with lilies?
I will post the answer in this comment section this evening.