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

using four eights (8) and a one (1) and one mathematical symbol , create the number 100

I am something people love or hate. I change peoples appearances and thoughts. If a person takes care of them self I will go up even higher. To some people I will fool them. To others I am a mystery. Some people might want to try and hide me but I will show. No matter how hard people try I will Never go down. What am I?

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

You can see it everyday, But cannot touch it at will. What is it?

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

A man is walking down a road with a basket of eggs. As he
is walking he meets someone who buys one-half of his eggs
plus one-half of an egg.
He walks a little further and meets another person who buys
one-half of his eggs plus one-half of an egg.
After proceeding further he meets another person who buys
one-half of his eggs plus one half an egg. At this point, he
has sold all of his eggs, and he never broke an egg.
How many eggs did the man have to start with?

What do you call a fish without an eye?

If,

A + B = C
D - C = A
E - B = C

Based on the above equations, find out the answer for:

D + F = ?

If you say my name, I will no longer exist. What am I?