Math Riddles

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?

Question: There are ten horses in a field. They each have a stable. There was a storm one day and struck one of the stables. The stable burned. There are now 9 stables. Every horse has to go in a stable at night. You can't build another stable and you can't fit 2 horses in one stable. How do you fit ten horses in 9 stables?

Question: There are five hen and rooster pairs. Each pair has one baby every month.

How many chickens will there be in one year?

Question: A rat is placed at the beginning of a maze and must make it to the end. There are four paths at the start that he has an equal chance of taking: path A takes 5 minutes and leads to the end, path B takes 8 minutes and leads to the start, path C takes 3 minutes and leads to the end, and path D takes 2 minutes and leads to the start.

What is the expected amount of time it will take for the rat to finish the maze?

Question: Which is the missing number in the below Number Series? 2, 3, 5, 7, 11, 13, ?, 19