CBSE Class 8 Annual Assessment

Annual assessment for Class 8 students under CBSE, focusing on advanced concepts in core subjects to prepare for higher secondary education.

Tales by Dots and Lines — Class 8 Mathematics

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Mathematics · 14 chapters
Summary, key terms, important questions and a practice quiz with AI diagnosis for each.

Chapter 6: Tales by Dots and Lines

Summary

This data-handling chapter deepens the ideas of mean and median and introduces line graphs. The mean is reinterpreted as a balance point: the total distance of values to its left equals the total distance to its right, and there is only one such centre. Including a value above the mean raises it, and below it lowers it; the same logic governs the median, the middle value of sorted data. Algebra shows that adding a fixed number \(k\) to every value raises the mean by \(k\), and multiplying every value by \(k\) multiplies the mean by \(k\). The mean and median can be found efficiently from frequency tables. Spreadsheets are introduced as a tool, with formulas like \(\text{SUM}\) and \(\text{AVERAGE}\) to compute totals and averages quickly. Line graphs visualise change over time — temperature, rainfall, space launches and sleep durations — and the chapter stresses reading a graph in two steps: first identify what is given (scale, axes, marks), then infer and interpret trends, comparing steepness to judge rates of change.

Mean as a balance pointMedian and changing dataMean and median with frequenciesSpreadsheetsLine graphs and interpreting data

Key terms

Mean
The sum of all values divided by their count; a balance point where total left and right distances are equal.
Median
The middle value of data arranged in order, with equally many values above and below it.
Balance point
The interpretation of the mean as the unique value equalising distances on both sides.
Frequency table
A table listing each value with how often it occurs, used to find mean and median efficiently.
Spreadsheet
A grid of cells where formulas like \(\text{SUM}\) and \(\text{AVERAGE}\) compute totals and averages.
Line graph
A graph of points joined by line segments, used to show change over time.

Important questions

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Practice quiz

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Class 8 Maths — Tales by Dots and Lines (Practice Quiz)

10 Qs · ~10 min