A GCSE-style histogram with unequal class widths: five gray bars for 0 < t ≤ 10, 10 < t ≤ 15, 15 < t ≤ 20, 20 < t ≤ 30 and 30 < t ≤ 50, so each bar’s area stands for its frequency. The vertical axis is titled Frequency density and numbered from 0 to 3 by 0.5, with each block split into fifths by minor gridlines, and the horizontal axis is titled Time (t minutes) and numbered at the bin edges 0, 10, 15, 20, 30 and 50.
