What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see? What is it?

In a science lab, a petri dish hosts a healthy colony of yeast for an experiment. Now every minute, all the yeast cells divide into two. At noon, there was just a single cell of yeast and at 1:22, the Petri dish was half full. Can you calculate when the dish will be full of yeast?

In case you were starting to feel confident, this one was meant for third graders in Vietnam. The answer is 66, but we don't blame you for scratching your head about how they got there.

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

What work can one never finish?

10 people came into a hotel with 9 rooms and each guest wanted his own room. The bellboy solved this problem.
He asked the tenth guest to wait for a little with the first guest in room number 1. So in the first room, there were two people. The bellboy took the third guest to room number 2, the fourth to number 3, ..., and the ninth guest to room number 8. Then he returned to room number 1 and took the tenth guest to room number 9, still vacant.
How can everybody have his own room?

Replace the question mark with the number below given a simple math problem.

A hen, a dog, and a cat are stolen. Three suspects are arrested named Robin, Steve, and Tim. The police are sure that all of them stole one of the animals but they don't know who stole which animal.

Sherlock Holmes is appointed to identify and is provided with the following statements from the investigation.

Robin - Tim stole the hen
Steve - Tim stole the dog
Tim - Both Robin and Steve are lying. I neither stole a hen nor a dog.

Sherlock is somehow able to deduce that the man who stole the cat is telling a lie and the man who stole the hen is telling truth.

Can you help him find out who stole which animal?

How many letters are in the alphabet?

I cry without having a voice.
I fly without having wings.
I bite without having teeth.
I whisper without a mouth.

Who am I?