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Class 8 Tales by Dots and Lines: cheat sheet
CBSE Mathematics. Organise data in frequency tables, find the mean, median, mode and range, and read line graphs to compare groups and spot trends.
Key ideas
- A frequency table counts how often each value or group of values occurs.
- In grouped data, a value on the boundary goes in the higher class (10–20 holds 10 but not 20).
- The mean is the total divided by the count; it is pulled by very large or small values.
- The median is the middle value after sorting; with an even count, average the two middle values.
- The mode is the most frequent value; the range (largest − smallest) shows the spread.
- A line graph shows how a quantity changes over time; a steeper line means a faster change.
- Use percentages to compare groups of different sizes.
Remember
| Mean | sum of values ÷ number of values |
| Median (n values) | the ((n + 1)/2)th value after sorting |
| Range | largest − smallest |
Watch out
- Finding the median without sorting the data first.
- Taking the highest frequency as the mode instead of the value that has it.
- Comparing raw counts for groups of different sizes.
Worked example
In five matches Meera scored 26, 33, 79, 13, 79 runs and Rohan scored 81, 60, 42, 28, 39. Compare their means and their ranges. Who was more consistent?
Working: a smaller range means the scores are closer together
Answer: Meera: mean 46, range 66; Rohan: mean 50, range 53; Rohan (smaller range)
Practise Tales by Dots and Lines
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