A histogram is drawn with equal class widths. The classes and frequencies are 0–20: 9, 20–40: 14, 40–60: 22 and 60–80: 11. Which class has the tallest bar, and what is its class mark?

Both look like bars, but they differ:

**Bar graph**: For DISCRETE / categorical data (favourite colour, sport, etc.). Bars have GAPS between them. Width has no meaning.

**Histogram**: For CONTINUOUS / grouped data with class intervals. Bars TOUCH (no gaps), reflecting that the class boundaries are continuous. Bar WIDTH represents class size; HEIGHT represents frequency.

**Frequency polygon**: connect the midpoints (class marks) of the tops of histogram bars to form a line graph. Useful for comparing two distributions on the same axes.

**Key rule**: histogram bars must have no gaps; bar graph bars MUST have gaps.