Math Riddles

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: 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: When I was 2 years old, my brother was half my age. Now I am 100 years old, how old is my brother?

Question: What temperature is twice as hot as 0 degrees Celsius?

Question: Why is 12 divided in half 7?