This deep dive covers Different Types of Class Intervals within Grouped Data for GCSE Mathematics. Revise Grouped Data in Statistics for GCSE Mathematics with 14 exam-style questions and 20 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 6 of 8 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Different Types of Class Intervals
Continuous Data (most common)
- Format: 10 ≤ x < 20, 20 ≤ x < 30
- Midpoint: (10 + 20) ÷ 2 = 15
- Class width: 20 - 10 = 10
Discrete Data
- Format: 1-5, 6-10, 11-15
- Midpoint: (1 + 5) ÷ 2 = 3
- Class boundaries: 0.5-5.5, 5.5-10.5, 10.5-15.5
Unequal Class Widths
Sometimes classes have different widths. Each interval is treated separately, but calculations follow the same principles.
Practice questions for Grouped Data
A frequency table uses the class intervals shown below. | Speed, s (mph) | Frequency | |---|---| | 0 < s ≤ 20 | 4 | | 20 < s ≤ 40 | 11 | | 40 < s ≤ 60 | 9 | | 60 < s ≤ 80 | 2 | A car travels at exactly 40 mph. Which class interval does this value belong to?
A teacher groups 30 students' test scores into four class intervals and calculates the estimated mean and estimated median. Explain why both the estimated mean and the estimated median from grouped data are only approximations of the true values. In your answer, refer to the assumptions made.