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 = <em>484</em>. <em> </em>484 is a perfect square.<em> yay !</em>
None of the other choices is a perfect square, because we already know that 23 squared is bigger than all of them.
