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

Two in a corner, one in a room, zero in a house, but one in a shelter. What am I?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

He digs out tiny caves and stores gold and silver in them. He also built bridges of silver and made crowns of gold. They are the smallest you could imagine. Sooner or later everybody needs his help, yet many people are afraid to let him help them. Who is he?

When it's bad luck to meet a black cat?

You measure my life in hours
I serve you by expiring
I vanish faster when I am thin
and slower when I am thick
The wind is my energy
What am I?

How many triangles are there in the picture below?

The product of three consecutive numbers is 7980.
Then the sum of these consecutive numbers would be?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

You need to remove two matchsticks to make the below equation true. Can you do it ?