Question: You have found a mutant algae that doubles in size every hour. It takes 18 hours for one algae plant to take up half of a certain lake.
How long would it take for two of these plants to take up half of the same lake?
Answer: 17 hours. At 17 hours the one plant will take up 1/4 of the lake (1/2 of 1/2). At 17 hours the two plants would be double the size of the one plant and double 1/4 is one half.