To simplify √125, we can factor it into a perfect square and a prime number:
√125 = √(25 × 5)
We know that √25 = 5, so we can simplify further:
√125 = √(25 × 5) = √25 × √5 = 5√5
Therefore, the simplified form of √125 is 5√5.
So the answer is option 3: 5√5.