The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

How many triangles are there on the puzzle below?

I make a loud sound when I’m changing. When I do change, I get bigger but weigh less. What am I?

I am not alive, but I grow; I don't have lungs, but I need air; I don't have a mouth, but water kills me. What am I?

John went to meet his friend Jacob, but when he was about to reach the main gate, John notices that Jacob had a mighty dog who was fastened to the tree. The chain is long enough that it allows the dog to reach the main gate.

How can the John reach the main gate?

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

One of the leprechaun is missing if you see the two pictures attached to this question. Where did he go? When he comes back, do you know where has he been?

If eleven plus two equals one, what does nine plus five equal?

One night, a man runs away from home. He turns left and keeps running. After some time he turns left again and keeps running. Later, he turns left one more time and runs back home—but when he gets home, he finds a man in a mask. Who was the man in the mask?

Why is the Hole below a Lock?