- A4
- B3
- C5
- D6
Step-by-Step Solution
The class 10–20 holds values from 10 up to but not including 20: 12, 18, 15 and 11, a frequency of 4. For the record, 0–10 holds 3, 7, 9 and 20–30 holds 25, 22, 28.
Answer: A) 4
The runs scored by 10 players were 3, 12, 25, 7, 18, 22, 9, 15, 28 and 11. The data is grouped using the classes 0–10, 10–20 and 20–30. What is the frequency of the class 10–20?
Class 9StatisticsStatistics and Probability
Key idea: Class intervals and class marks
When data has many distinct values (like heights or weights), group it into **class intervals**.
Example table:
| Class interval | Frequency |
|---|---|
| 0–10 | 5 |
| 10–20 | 8 |
| 20–30 | 4 |
**Class mark** of an interval = (lower limit + upper limit) / 2.
For 0–10: mark = 5. For 10–20: mark = 15.
**Inclusive vs exclusive intervals**:
- Exclusive (continuous) form like 0–10, 10–20: 10 belongs to the SECOND interval, not the first.
- Inclusive form 0–9, 10–19: rare in modern textbooks — convert to continuous form (subtract 0.5 from lower, add 0.5 to upper) before drawing histograms.
Example table:
| Class interval | Frequency |
|---|---|
| 0–10 | 5 |
| 10–20 | 8 |
| 20–30 | 4 |
**Class mark** of an interval = (lower limit + upper limit) / 2.
For 0–10: mark = 5. For 10–20: mark = 15.
**Inclusive vs exclusive intervals**:
- Exclusive (continuous) form like 0–10, 10–20: 10 belongs to the SECOND interval, not the first.
- Inclusive form 0–9, 10–19: rare in modern textbooks — convert to continuous form (subtract 0.5 from lower, add 0.5 to upper) before drawing histograms.
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