Me
which of the following numbers is a perfect square?
484
485
489
490

Let me show you how you could have answered this question
without using your computer:

Try out different numbers:

Guess a number. 
Square it. 
- If the result is less than one of the choices, try a larger number.
- If the result is more than one of the choices, try a smaller number.
- If the result is equal to one of the choices, then that choice is a perfect square.

Try 10.
10 squared =100. 
Too small.  Try bigger.

Try 20.
20 squared = 400. 
Still too small, but getting close.  Try bigger.

Try 25.
25 squared = 625
Too big. Try smaller.

Try 23.
23 squared = 529.
Still too big.  Try smaller.

Try 21.
21 squared = 441.
Too small, but look where you are now: 
21 is too small, and 23 was too big.
Does that give you any ideas ?
What do you think you should try next ?

Try 22.
22 squared = 484.                         
484 is a perfect square.                    yay !

None of the other choices is a perfect square, because we
already know that 23 squared is bigger than all of them.