Good Riddles

Question: A box of marbles costs $20. If the marbles are worth $19 more than the box, what is the box worth?

Question: There are 31 horses on a cliff, first they jump into the air, then they come down and stop, then they stand still.

Why do they do this?

Question: At low tide 14 rungs of a ship are above the water, the rungs are 15 centimeters apart. each 15 mins the water rises 15 centimeters. after 2 hours and 30 mins how many rungs are above the water?

Question: One day there was a man in a hospital bed, and there was a man sitting next to him. So, the doctor asked the man sitting next to the man in the hospital bed, he asked, who are you? The man said listen closely for I will only tell you this once. Brothers and sisters I have none, but this man's father is my father's son. Who is this man?

Question: You have three coins. One always comes up heads, one always comes up tails, and one is just a regular coin (has equal change of heads or tails). If you pick one of the coins randomly and flip it twice and get heads twice, what is the chance of flipping heads again?