It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

The more you take me, the more you leave me behind.
Who Am I?

How can you drop a raw egg from a height onto a concrete floor without cracking it?

How is the moon similar to a dollar?

John gave half of the apples he had plus one more to Jacob. He gave half of the remaining ones plus one more to James. Now, John was left with just one apple.

Can you find out how many did he have in the beginning?

If a zookeeper had 100 pairs of animals in her zoo, and two pairs of babies are born for each one of the original animals, then (sadly) 23 animals don’t survive, how many animals do you have left in total?

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

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.

Most people think of me as money. But when they find me in the water, they won’t get any money out of me. What am I?

A chess tournament is taking place on knock-out terms (the one who loses the match is out of the game).
(a) If 10 matches are played in total, how many players participated?
(b) If 20 players took part in the tournament, how many matches were played?