Chapter 12 — Tales by Dots and Lines

Chapter 12 of the Class 8 Maths NCERT textbook (Ganita Prakash), "Tales by Dots and Lines", teaches data visualization and statistical measures through dot plots and line graphs. Students learn how mean and median represent the 'centre' of data, how they change when values are added or removed, and how to visualize trends over time using line graphs and infographics.

• Mean and median as centres — Using dot plots, the chapter builds intuition for mean and median as measures of a dataset's centre, and studies how each responds when values are added, removed, or shifted and scaled by a constant.
• Line graphs for change over time — Line graphs are introduced as a clearer way than column graphs to show how data evolves across time, especially for large datasets where trends matter more than individual bars.
• Tools for real data — Spreadsheet formulas handle large datasets efficiently, and infographics use colour and visual encoding to compare figures across regions or categories at a glance — statistics meeting practical presentation.

1. 01Mean represents the 'centre' of data where total distances from values on the left equal total distances on the right
2. 02When a value greater than the mean is added, the mean increases; when a value less than the mean is added, the mean decreases
3. 03If all data values are increased by a fixed number, the mean also increases by that same fixed number
4. 04If all data values are multiplied by a fixed number, the mean is also multiplied by that same fixed number
5. 05Median of a dataset is the middle value; adding a value greater than median increases the median, adding one less than median decreases it
6. 06Line graphs effectively visualize data changes over time better than column graphs for large datasets
7. 07Spreadsheets use formulas like =SUM(range) and =AVERAGE(range) to quickly calculate statistics from data tables
8. 08Infographics use color scales and visual encoding to compare data across regions or categories at a glance