To find the relative frequency of a non-defective unit, we first determine the number of non-defective units.
Given:
- Total units checked = 500
- Non-functioning units = 25
The number of non-defective units is: \[ 500 - 25 = 475 \]
The relative frequency of a non-defective unit is the ratio of non-defective units to the total units: \[ \text{Relative Frequency} = \frac{475}{500} \]
Now we can simplify the fraction \( \frac{475}{500} \):
- Both the numerator and denominator can be divided by 25: \[ \frac{475 \div 25}{500 \div 25} = \frac{19}{20} \]
Thus, the relative frequency of a non-defective unit in simplest form is: \[ \frac{19}{20} \]
Therefore, the correct answer is: \( \frac{19}{20} \).