What goes up but never comes down?

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"

What does this below rebus puzzle mean?

A chicken farmer has figured out that a hen and a half can lay an egg and a half in a day and a half. How many hens does the farmer need to produce one dozen eggs in six days?

Find the 8 in the below-given Image.

Can you find out the remainder when 3^300 is divided by 5?

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?

O_er_t_o_

Complete the missing letters of the given word.