If the units digit of a perfect square is 5 then the units digit of its square root is _________

Answer

To solve the problem, we need to determine the units digit of the square root of a perfect square that has a units digit of 5.

### Step-by-Step Solution:

1. **Understanding Perfect Squares**:
A perfect square is a number that can be expressed as the square of an integer. For example, \(1^2 = 1\), \(2^2 = 4\), \(3^2 = 9\), \(4^2 = 16\), \(5^2 = 25\), etc.

2. **Identifying Units Digits**:
We need to focus on the units digits of these perfect squares. The units digits of perfect squares can be 0, 1, 4, 5, 6, or 9.

3. **Focusing on Units Digit 5**:
We are specifically interested in perfect squares that end with the digit 5. The only integer whose square ends with 5 is 5 itself.

4. **Calculating the Square**:
Let's calculate the square of 5:
\[ 5^2 = 25 \]
Here, the units digit of 25 is 5.

5. **Finding the Square Root**:
Now, we find the square root of 25:
\[ \sqrt{25} = 5 \]
The units digit of the square root (which is 5) matches the units digit of the original perfect square (which is also 5).

6. **Verifying with Other Examples**:
Let's check another example:
- Consider 15:
\[ 15^2 = 225 \]
The units digit of 225 is 5. Now, the square root:
\[ \sqrt{225} = 15 \]
The units digit of 15 is also 5.

- Another example is 25:
\[ 25^2 = 625 \]
The units digit of 625 is 5. The square root:
\[ \sqrt{625} = 25 \]
The units digit of 25 is again 5.

7. **Conclusion**:
From the examples above, we can conclude that if the units digit of a perfect square is 5, then the units digit of its square root is also 5.

### Final Answer:
The units digit of its square root is **5**.