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

No matter how little or how much you use me, you change me every month. What am I?

Solve the mathematical equation in the picture below.

Count The number of F's in the paragraph below:

"FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS"

Prove that twice of ten is the same as twice of eleven.

What has to be broken before you can use it?

I have two sand hourglasses:
1. A 7 minute one and
2. An 11-minute one.

Using just these 2 sand hourglasses, how can I measure time as 15 minutes?

How old is your son? asked a man to his neighbour. My son is five times as old as my daughter and my wife is five times as old as my son. I am twice as old as my wife whereas my grandmother, who is celebrating her eighty-first birthday is as old as all of us put together.

How old is the man's son ?

Can you find the odd number in the following?

2716, 4135, 5321 and 7145

You can hear me, but you can't touch or see me.

What am I?