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

Using Only Five 5's and any mathematical operator make sum as 37

Can you find the missing piece of the Porsche?

A mad serial killer kidnaps people and forces them to play the game of 2 pills with them, In this game, there are pills in the table and one of them is normal pill while the other one is deadly poisonous.
The victim will choose one pill and the killer will pick the other pill and both simultaneously will swallow the pill with water.
victim dies every time.

One day the serial killer kidnaps the Joseph and forces him to play the same game with him.

Joseph solves the mystery of the two pills and remains alive.

Explain?

When Jack was six years old he hammered a nail into his favourite tree to mark his height. Ten years later at age sixteen, Jack returned to see how much higher the nail was. If the tree grew by five centimetres each year, how much higher would the nail be?

When we see 2 but call 10?

Take away my first letter, then take away my second letter. Then take away the rest of my letters, yet I remain the same. What am I?

How many times can you subtract the number 5 from 25?

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

Five thieves looted a bank and they ran away in a car. The bank staff informed the police and they began the search of their car in their jeep. They found them on a road and chased them eventually catching them. The light that is used to fill the number plate was broken on the thieves' car. Also, the headlights of the jeep police were not working. How were the police able to catch the thieves then?