Class types organize continuous data into intervals. Inclusive classes: [a, b] includes both endpoints (mainly used in India). Exclusive classes: [a, b) includes lower, excludes upper (international standard). Class width: difference between upper and lower boundaries. Class mark/midpoint: (lower + upper)/2, used in calculations. Key concepts: determine appropriate number of classes (typically 5-20), ensure equal width. Common traps: inconsistent class boundaries, unclear overlaps, inappropriate width. Exam tips: verify class continuity, check data coverage. Time-saving: use width formula: (max - min) / number of classes. Applications: age groups, income ranges, test scores. Class intervals: mutually exclusive and exhaustive. Frequency distribution: tally marks or count in each class. Understanding class construction essential for grouped data analysis. Practice with real datasets.