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

Give it food and it will live; give it water and it will die.

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

What brings you down but never up?

In front of you, there are 9 coins. They all look absolutely identical, but one of the coins is fake. However, you know that the fake coin is lighter than the rest, and in front of you is a balance scale. What is the least number of weightings you can use to find the counterfeit coin?

Solve this riddle by finding the odd one out from the rest.

What Does this text mean:

important=important

What can run but never walks, has a mouth but never talks, has a head but never weeps, has a bed but never sleeps?

What does an Island and the letter T have in common?

Make a sentence consisting of three words that have the whole alphabet.