1. **State the problem:** We need to apply Sturges' rule to find the number of classes for a dataset with 400 observations, then calculate the class width given the range is 60. 2. **Formula for Sturges' rule:** $$k = 1 + \log_2(n)$$ where $k$ is the number of classes and $n$ is the number of observations. 3. **Calculate the number of classes:** $$k = 1 + \log_2(400)$$ Since $\log_2(400) = \frac{\log_{10}(400)}{\log_{10}(2)} \approx \frac{2.60206}{0.30103} \approx 8.64,$ $$k = 1 + 8.64 = 9.64$$ We round $k$ to the nearest whole number, so $k = 10$ classes. 4. **Calculate class width:** Class width $w$ is given by $$w = \frac{\text{Range}}{k} = \frac{60}{10} = 6$$ 5. **Final answer:** Number of classes = 10 Class width = 6 This means the data should be divided into 10 classes, each with a width of 6 units.