To find the relative frequency of a non-defective unit, we first need to determine the number of non-defective units.
Since there are 500 units in total and 25 have non-functioning keys (defective), the number of non-defective units is:
\[ 500 - 25 = 475 \]
Now, the relative frequency of a non-defective unit is calculated by taking the number of non-defective units and dividing it by the total number of units:
\[ \text{Relative frequency} = \frac{\text{Number of non-defective units}}{\text{Total number of units}} = \frac{475}{500} \]
Next, we simplify the fraction \(\frac{475}{500}\). To do this, we find the greatest common divisor (GCD) of 475 and 500, which is 25:
\[ \frac{475 \div 25}{500 \div 25} = \frac{19}{20} \]
Thus, the relative frequency of a non-defective unit in simplest form is:
\[ \frac{19}{20} \]
The correct response is:
Start Fraction 19 over 20 End Fraction