Which is the rope you never skip with?

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

What jumps when it walks and sits when it stands?

If I put in one bird per cage, I have one bird too many. If I put in two bird per cage, I have one cage too many. How many cages and birds do I have?

Move three sticks of the spiral below to form a square.

If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on similar logic, Can you prove that the below algebraic equation is true?
11 - 1 = 10 ?

People make me, save me, change me, raise me. What am I?

In the given figure, move three matchsticks so that the resulting figure contains two rectangles.

In two decks of cards, what is the least amount of cards you must take to be *guaranteed* at least one four-of-a-kind?

Can you name an animal whose killing cannot be performed without spilling your own blood?