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?
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.