Can you convert the number zero(0) into a positive number using just one mathematical operator ?

I am a three digit number.
My tens digit is five more than my ones digit.
My hundreds digit is eight less than my tens digit.
What number am I?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?

I have Rs.50 and I spend it in the way as below.

Find three numbers such that

* When we multiply three numbers, we will get the prime numbers.
* The difference between the second and the first number is equal to the third and second.

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?

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

Solve the riddle below:

If a Chicken says, 'All chickens are liars" is the chicken telling the truth?

In the Chess Board picture below white army is arranged. You need to add a black army on the board such that no piece is under any threat.
Note: Army comprised of 1 king, 1 queen, 2 rooks, 2 bishops, 2 knights, and 8 pawns.

If EELS + MARK + BEST + WARY = EASY

What does HELP + BARK + WARD + LEAD equal?