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Chapter 12 · Tales by Dots and Lines

NCERT Class 8 · Ganita Prakash

← Contents
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CHAPTER 12 OF 14

Tales by Dots and Lines 📈

A graph is a story told with dots and lines. Reading one well means knowing what each axis measures before you look at the shape.

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Part 1 · Kinds of Graph

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Part 2 · Pie Charts

🗺️

Part 3 · Coordinates

1

Which graph for which job 📊

Choosing the wrong kind of graph is a favourite exam question. Each one answers a different question.

📊 Match the graph to the job

GraphBest forExample
Bar graphcomparing separate thingsmarks of five students
Pie chartshowing parts of one wholehow a day is spent
Line graphshowing change over timetemperature through the day
Histogramgrouped data, bars touchingheights in ranges
Pictographsimple counts with symbolsbooks read each month
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Bar graph or histogram? A bar graph has gaps between the bars because the categories are separate. A histogram has no gaps, because the data is grouped into continuous ranges.

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Game 1 — Which Graph?

2

Pie charts 🥧

A whole circle is 360° and also 100%. Every pie-chart question moves between those two.

🥧 Converting

To findDo this
Angle from a percentagepercentage ÷ 100 × 360
Angle from a fractionfraction × 360
Percentage from an angleangle ÷ 360 × 100
Quantity from an angleangle ÷ 360 × total
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Useful landmarks: a quarter is 90°, a half is 180°, a third is 120°, and 10% is 36°. Spotting one of these saves the calculation entirely.

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Game 2 — Pie Chart Angles

3

The coordinate plane 🗺️

Two number lines crossing at right angles let you name any point with a pair of numbers.

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Order matters: (x, y). The first number is along the x-axis (across), the second is up the y-axis. The point (3, 5) is not the same as (5, 3). "Along the corridor, then up the stairs."

🗺️ The four quadrants

QuadrantxyExample
I++(3, 5)
II+(−3, 5)
III(−3, −5)
IV+(3, −5)
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The origin is (0, 0). A point on the x-axis has y = 0, like (4, 0). A point on the y-axis has x = 0, like (0, 7).

✍️

Game 3 — Read the Coordinates

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Topic Mock Test

12 questions on graphs and coordinates. Read the axes first. 🍀

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Chapter 11 · Geometric Themes 🔺

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Chapter 13 · Algebra Play 🧮