Z Score Calculation 955D31
1. **Problem statement:**
You scored better than 35% of the students on an exam where scores are normally distributed with mean $\mu=62$ and standard deviation $\sigma=12$. We want to find your z-score and then determine your actual exam score.
2. **Formula and rules:**
The z-score formula is:
$$z=\frac{X-\mu}{\sigma}$$
where $X$ is the exam score.
The z-score corresponds to the number of standard deviations a value is from the mean.
3. **Find the z-score for the 35th percentile:**
The percentile rank means the cumulative area under the normal curve to the left of your score is 0.35.
Using a standard normal table or calculator, the z-score for 0.35 cumulative probability is approximately:
$$z \approx -0.385$$
4. **Calculate the actual exam score $X$:**
Rearranging the z-score formula:
$$X = z \times \sigma + \mu$$
Substitute values:
$$X = (-0.385) \times 12 + 62 = -4.62 + 62 = 57.38$$
5. **Interpretation:**
Your exam score is approximately 57.38, which means you scored better than 35% of the students.
6. **Graph description:**
The normal curve is centered at 62 with standard deviation 12. The area to the left of $X=57.38$ (z = -0.385) is shaded to represent your ranking.
Final answer:
Your z-score is approximately $-0.385$ and your exam score is approximately $57.38$.