Good Riddles

Question: Enter one hole and leave three,
once you succeed I'm on thee?

What am I?

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: John has three daughters who are all unmarried. The youngest always lies, the oldest always tells the truth, and the one in the middle either tells the truth or lies. A very rich young man comes to John's house and says he wishes to marry one of his daughters. Naturally he wants to marry the oldest or the youngest so he will always know if she is lying or telling the truth. John agrees but says he can only ask one of the girls a yes or no question to decide which one he marries. They all look the same age.

What one question does he ask one of the daughters at random to figure out which daughter is the youngest or oldest?

Question: I have a tongue but cannot taste.
I have a soul but cannot feel.

What am I?

Question: I may be of the eye,
in order I am pie,
in my center there is a star,
I keep medics where they are.

What am I?