I’m tall when I’m young, and I’m short when I’m old. What am I?

If you say my name, I will no longer exist. What am I?

A wooden log balances equally on the scales when weighed with three-quarters of a pound and three-quarters of a wooden log.

Can you calculate the weight of the entire wooden log?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

I am the fastest animal but cannot climb the tree. What am I?

What has to be broken before you can use it?

How many letters are in the alphabet?

John was piloting a plane behind a car but was never able to overtake it. Why?

What has many keys but can’t open a single lock?

What breaks yet never falls, and what falls yet never breaks?