Graphs & Statistics Clinic: WASSCE Core Maths Graph Lessons

Graphs carry a lot of marks in WASSCE Mathematics, and they lose a lot of marks too. Not because students can’t draw, but because one small skill in the chain is weak: the scale, the plotting, the reading or the interpretation.

The Graphs & Statistics Clinic takes those skills one at a time. Each lesson finds one gap, explains why it happens, and gives you practice to fix it, with diagrams you can follow on your phone. New lessons appear here every day.

What you’ll be able to do by the end

choose a scale that fits and is easy to read
plot points and complete tables of values without sign errors
draw straight lines and smooth quadratic curves accurately
read values from a graph in both directions, with guide lines
find and explain the gradient and the intercepts
build a cumulative frequency curve and read the median and quartiles
protect every mark point in a WASSCE graph question

Graph work in one page

Almost every Core Maths paper has a graph question, and it carries marks at several points: the table, the scale, the plotting, the curve, the readings and the interpretation. Here is the whole skill in seven pictures. Each lesson below fixes one step properly.

The seven graph skills: read, choose the axes, plan the scale, label, plot, draw, read and interpret — Seven skills sit inside every graph question.

1. Plan the scale

Find the range, divide by the number of large squares, and round up to a friendly number such as 1, 2, 5 or 10.

Four steps to choose a graph scale: find the range, count large squares, divide, round up to a friendly number such as 10 — Range, squares, divide, round up.

2. Plot accurately

Across first (x), then up or down (y). Check the signs and the quadrant before you mark the point.

Points A(4, 3), B(−2, 5), C(3, −4) and D(−1, −3) plotted by moving across first, then up or down — Across first, then up or down.

3. Draw the right line or curve

Rule one straight line through linear points. Draw one smooth curve through quadratic points, rounded at the turning point.

Graph of y = x² − 2x − 3 showing roots −1 and 3, y-intercept −3, turning point (1, −4) and axis of symmetry x = 1 — Roots, y-intercept, turning point and axis of symmetry.

4. Read values with guide lines

Start on the axis of the value the question gives you, rule a line to the graph, then to the other axis.

Rice cost graph: from 4 kg up to the line and across gives about GH₵60; from GH₵45 across to the line and down gives about 3 kg — Start on the axis of the given value.

5. Find and explain the gradient

\text{Gradient} = \frac{\text{change in } y}{\text{change in } x}

Line through A(2, 3) and B(6, 11) with run 4 and rise 8, so the gradient is 2 — Rise over run, from two clear points.

6. Statistics: the cumulative frequency curve

Plot running totals at the upper class boundaries, draw a smooth rising curve, and read the median from n ÷ 2 on the cumulative frequency axis.

Cumulative frequency curve with guide lines from 20, 40 and 60 giving Q1 about 36.5, median about 47.5 and Q3 about 58 — Median and quartiles start on the CF axis.

The lessons

Graphs in Mathematics: 6 Mistakes Students Must Avoid

📚 Part of the Graphs & Statistics Clinic: every lesson on this topic, in one place. In many Ghanaian SHS classrooms, the moment a Mathematics question says “draw the graph” or “use your graph to find,” some learners become quiet. Not because they do not know anything. Many of them know the formula. They can… Start this lesson →

Practise as you go

After each lesson, try the graph reading questions and the statistics questions in the Practice Zone.

Not sure where your graph work breaks down? Start with Find My Gap.

The graph mistakes examiners see most

Mistake	Fix
Scale chosen after plotting starts, or changed halfway	Plan one scale for each axis first
(x, y) plotted as (y, x)	Across first, then up
Quadratic points joined with a ruler	One smooth curve, rounded at the bottom
Values read by eye	Ruled guide lines, counted small squares
Frequencies plotted instead of cumulative totals	Running totals at upper class boundaries
No units or interpretation	Say what the value means, with its unit

Questions learners often ask

How do I choose a scale for a graph?

Divide the range of values by the number of large squares available, then round up to 1, 2, 5, 10 or 20 units per square.

How do I find the median from a cumulative frequency curve?

Find n ÷ 2, start at that value on the cumulative frequency axis, go across to the curve, then down to read the value.

Where are the roots on a quadratic graph?

Where the curve crosses the x-axis, because y = 0 there.

This clinic is part of How to Pass WASSCE and NOVDEC Core Maths.

Sources and further reading

These lessons are built on what WAEC examiners report year after year, matched to Ghana’s SHS curriculum.

WAEC Chief Examiner’s Reports: the yearly reports on where candidates lose marks
NaCCA SHS curriculum: the official Ghana Senior High School curriculum
Ghana curriculum resources: official teaching and learning resources

Written by Dickson Sarpong

NTC-certified SHS Mathematics teacher in Ghana with WAEC marking experience, and author of The Bridge Series textbooks. Every lesson here is built around the mistakes WAEC examiners keep reporting.

About Dickson Stuck? Ask a question

The Bridge Series: The Bridge to Mathematics and The Bridge to Additional Mathematics for SHS

Want the whole topic, step by step? My textbooks, The Bridge to Mathematics and The Bridge to Additional Mathematics for SHS, follow the new curriculum and rebuild the basics as you go.

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Graphs & Statistics Clinic