Cumulative Frequency summary

Key learning points

• Plot upper-class boundaries against running totals; join with a smooth curve.
• Median at total$/2$; Q1 at total$/4$; Q3 at $3\times$total$/4$.
• IQR = Q3 − Q1 measures spread of the middle half.

Worked example 1 — Reading the median

CF graph, $n=80$. CF height for the median?

Working

Read across from $n/2$.

Worked example 2 — IQR

UQ $=12$, LQ $=5$. IQR?

Working

UQ − LQ.

Worked example 3 — Plotting

CF is plotted against which x-value?

Working

Running total to the end of the class.

Scaffolded Learning Sheet and answers (PDFs)

This page is a short, searchable overview for revision and search engines. Use the Scaffolded Learning Sheet first, then the Answers PDF for a full written solution. The printable PDFs remain the main classroom resource.