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

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

Can you count the number of triangles in the given picture?

A woman lives in a Tall building thirty-six floors high and served by several elevators which stop at each floor going up and down. Each morning she leaves her apartment and goes to one of the elevators. Whichever one she takes is three times more likely to be going up than down. Why?

Its something that each of us devours,
Not just us but birds, beats, trees, and flowers,
Frets iron and nibbles steel,
Toil hard stones to meal,
Exterminates king, collapse town,
And blows the mountains down.

How many words can a pen with half refill write?

John is asked to stand behind Jacob and Jacob is asked to stand behind John. Both of them feel confused about it and don't know what to do?

But it is quite possible, do you know how?

Can you write down eight eights so that they add up to one thousand?

Take away the whole and some still remain. What is it?

Find the combined weight of the Cat, Dog and Rabbit in the given picture.