Tales by Dots and Lines | Mathematics Grade 8 CBSE

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From a dot to a story

A pair of numbers becomes a point; points become a line; the line tells a tale. Tap each idea to see how dots and lines carry information.

Explore · Dots and linestap an idea

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The three big ideas

The axes — a horizontal x-axis and a vertical y-axis cross at the origin (0, 0).
An ordered pair (x, y) locates a point: go x units right, then y units up. The order matters — (3, 5) is not (5, 3).
Points on an axis: (4, 0) sits on the x-axis; (0, 4) sits on the y-axis.
Plotting turns a table of numbers into dots you can see and compare.

Worked example. Plot the point (3, 2) and say where it lands.

1. Start at the origin (0, 0).

2. The x-coordinate is 3 → move 3 units right along the x-axis.

3. The y-coordinate is 2 → move 2 units up.

4. Mark the dot. It lands inside the grid, 3 across and 2 up — that is the point (3, 2).

Common mistake: swapping the numbers — going up first or reading (3, 2) as "3 up, 2 right". Always read x (right) before y (up).

A line graph plots points and joins them, showing how a quantity changes as time (or another variable) moves along the x-axis.
Reading the shape: a line going up means increase, down means decrease, flat means no change.
Steepness = rate: a steeper segment means faster change; a gentle slope means slow change.
Straight-line patterns: if y is always a fixed multiple of x (say y = 2x), the points line up perfectly straight.

A bar graph uses bars of equal width whose heights show amounts — perfect for comparing separate categories (fruits sold, marks by subject).
A double bar graph places two bars per category, so you can compare two data sets — like this year's rainfall against last year's.
Reading a value: find the top of the bar (or the point on a line), then read straight across to the y-axis scale.
Choosing the graph: a line graph for change over time; a bar graph to compare distinct groups.

Where you'll meet it

Graphs that tell stories

The fever chart

A hospital plots a patient's temperature against time. A line climbing then dropping tells the doctor the fever peaked and is breaking — a story read straight off the dots and lines.

Weather & monsoon

Newspapers show monthly rainfall as a bar graph. Tall bars in July and August make the monsoon obvious at a glance, and a double bar graph compares this year with the last.

Maps & locations

Map apps and seat numbers in a hall both use coordinate ideas — a row and a column, like an ordered pair, to pin down one exact spot among thousands.

Check yourself

Competency quiz

Modelled on the competency-based pattern — MCQ, assertion–reason and a case study, testing whether you can use the ideas, not just recall them.

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