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

What is black when you buy it, red when you use it, and gray when you throw it away?

If I put in one bird per cage, I have one bird too many. If I put in two bird per cage, I have one cage too many. How many cages and birds do I have?

The following "Brain Bat" means Slow Down.
S
L
O
W

Using the same logic, can you tell us what does the following Brain Bat means ?
E
V
I
G

Where do fish keep their money?

A mathematician couple was having a Frappuccino in Starbucks sitting opposite to each other. Suddenly the guy noticed the text written on the paper in front of them and exclaimed that it was wrong. The girl denied it and said it is appropriate. Both are correct. What is written on the paper?

Why is the Hole below a Lock?

Can you count the number of seconds in a year?

Clue: You need to bother about calculation.

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

Can you place six X (crosses) in below board without making three in a row in any way ?