Logic 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: If a farmer has 5 chickens, two horses, and a wife.

How many feet are on his farm?

Question: What single line can you add to the following statement to make it true?

5+5+5=550

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 man wants to buy a used car. He finds a beautiful Buick for $9500, but he buys it without paying a dime.

How did he manage this?