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.