Good Riddles

 
Swimming! (medium)

Question: 20 people jump into an empty swimming pool but 24 heads come up. How did this happen?

Question: What is as ancient as the earth but new every month?

Question: Which gate can you not go through?

Calendar (medium)

Question: What was the calendar so cramped up and going crazy?

Question: I have two rings. I move by request. If the mixture isn't right I just sit and rest.

What am I?