Histogram
A graphical representation of grouped continuous data using rectangular bars where the area of each bar is proportional to the frequency. The x-axis shows class intervals and the y-axis shows frequency density (frequency/class width).
Real World
Public Health England uses histograms with unequal class widths to display the age distribution of COVID-19 cases, with narrower bars for children (0–4, 5–11) and wider bars for older adults (65–80).
Exam Focus
Always label the y-axis as frequency density, not frequency — and calculate it as frequency ÷ class width for every bar.
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