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

I am a number I am not an odd number I am higher than 90 I am not higher than 100 If you subtract me from 100, you get nothing. What number am I?

Can you find the ages of a son, father and grandfather based on the following facts?
The sum of the ages of grandfather, father and son is 140 years.
The age of the son in months is the same as the grandfather in years.
The age of the son in days is the same as the father in weeks.

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

I am an odd number. Take away a letter and I become even. What number am I?

John replied, when asked how old he was. In 2 years he will be twice as old as he was five years ago.' How old is he ?

You need to arrange three 7 and mathematical symbols to form number 1?

Place a mathematical symbol between the numerals 5 and 9 in such a way that the resulting number is greater than 5 but smaller than 9.

If one and a half boys, eat one and a half burgers in one and a half hours.

How many burgers can 9 boys eat in 3 hours?

If we add four times the age of John four years from now to five times his age five years from now we get ten times his current age.

How old will John be two years from now?