Theory question 105
StatisticsThe table shows the distribution of the weights (Newtons) of 100 blood donors.
Weight (N): 55 − 59, 60 − 65, 66 − 71, 72 − 78, 79 − 86, 87 − 90
Number of donors: 18, 5, 20, 22, 27, 8
Draw a histogram for the distribution.
Show the model answer
Model answer
Class boundaries and widths: 54.5–59.5 (5), 59.5–65.5 (6), 65.5–71.5 (6), 71.5–78.5 (7), 78.5–86.5 (8), 86.5–90.5 (4).
The widths are unequal, so bar heights are frequency densities (frequency ÷ width): 3.6, 0.83, 3.33, 3.14, 3.38, 2.0.
Draw adjacent bars on the class boundaries with these heights; label axes (weight in N; frequency density) and give a scale.
Explanation
With unequal class widths, the area (not the height) of each bar shows the frequency.