Class 9 · Ganita Manjari
Unit 10 · Class 9Ganita Manjari
How Quantities Combine: Understanding Data
Organising raw data, frequency distributions, and the three big averages: mean, median, mode.
Lessons
3 concepts
- 1From Raw Numbers to a StoryA list of 30 exam scores tells you little. A frequency table (0-10, 10-20, …) suddenly reveals whether the class is bunched up or spread out. That is the whole point of data handling: turn noise into a story.
- 2Choosing the Right AverageMean is great when data is roughly symmetric. Median is a better summary when there are outliers (one student scoring 100 on a test where the rest scored 20-30). Mode is what you want for categorical data — "which flavou…
- 3Spread — Why Two Classes with the Same Mean Feel Very DifferentTwo classes can share a mean of 60, but one has scores 55-65 and the other 20-100. Range is the crudest way to see this; standard deviation (Class 11) sharpens it.
Skills to practise