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

You are given a cube that is made with the help of 10x10x10 smaller cubes summing up to a total of 1000 smaller cubes. You are asked to take off one layer of the cubes.
How many remain now?

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

A prisoner is told: "If you tell a lie, we will hang you and if you tell the truth, we will shoot you." What did the prisoner say to save himself?

You see a mathematical expression in the picture. Can you think of a movie that this expression refers to?

How many triangles are there on the puzzle below?

I have holes on the top and bottom. I have holes on my left and on my right. And I have holes in the middle, yet I still hold water. What am I?

Which English verb becomes past tense just by rearranging the letters?

This puzzle is for Harry Potter fans. Do you know why Tom Riddle is called Lord Voldemort?

Can you make a six-letter word using the letters N, A and B ?