1. **State the problem:** We are given that the experimental probability of a book reader having a defective backlight is $\frac{1}{x}$. We need to find the value of $x$. 2. **Understand the concept:** Experimental probability is calculated as the ratio of the number of favorable outcomes to the total number of trials. It is given by: $$\text{Experimental Probability} = \frac{\text{Number of favorable outcomes}}{\text{Total number of trials}}$$ 3. **Given:** Experimental probability = $\frac{1}{x}$. 4. **Interpretation:** The probability $\frac{1}{x}$ means that out of $x$ trials, 1 trial results in a defective backlight. 5. **Finding $x$:** To find $x$, we need the actual experimental data (number of defective backlights and total trials). Since the problem does not provide these, $x$ remains a variable representing the total number of trials per defective backlight. 6. **Conclusion:** Without additional data, $x$ is the denominator in the probability fraction $\frac{1}{x}$ representing the total number of trials per defective backlight. **Final answer:** $x$ is the total number of trials corresponding to one defective backlight, so $x$ is the denominator in the probability $\frac{1}{x}$.