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

What is the next number in the series?

15 29 56 108 208 ?

What am I?

Can you decipher the two rows to find the hidden word?

In the picture that is attached with this question, you can find a square which comprises of four little squares inside it. Consider this square to be made with matchsticks. You have to remove two matchsticks such that only two squares remain instead of five.How will you do it ?

What has many keys but can’t open a single lock?

Below toothpicks/matchsticks indicate the group of fishes moving from west to east direction. Can you make them move from east to west by just moving three toothpicks/matchsticks?

What mathematical symbol can be put between 5 and 9, to get a number bigger than 5 and smaller than 9?

Railroad Crossing, look out for the cars. Can you spell that, without any R's ?

You are given with the following sum. Each of the letters can be decoded as a digit. If we tell you that D = 5, then can you solve it entirely?

DONALD
+GERALD
=ROBERT