Exercise 2: Clean and describe

Using employee_survey.csv:

1. Count employees by department.
2. Calculate mean age, tenure, workload, and performance.
3. Count missing values in every column.
4. Create remote_mode: On-site (0 days), Hybrid (1–3), Mostly remote (4–5).
5. Compare mean performance across training_group.
6. Draw a histogram of performance.
7. Draw a boxplot of performance by training group.
8. Write two descriptive sentences without making causal claims.