Theory question 113
StatisticsThe table shows the frequency distribution of the ages of patients in a clinic.
Age (years): 17 − 19, 20 − 22, 23 − 28, 29 − 34, 35 − 43
No of patients: 6, 9, 12, 18, 18
(a) Draw a histogram for the distribution. (b) Find, correct to two decimal places, the mean age of the patients.
Show the model answer
Model answer
(a) Boundaries 16.5, 19.5, 22.5, 28.5, 34.5, 43.5 (widths 3, 3, 6, 6, 9). Plot frequency density (per 3 years): 6, 9, 6, 9, 6, as touching bars.
(b) Class marks 18, 21, 25.5, 31.5, 39; Σf = 63; Σfx = 108 + 189 + 306 + 567 + 702 = 1872.
Mean = 1872/63 ≈ 29.71 years.
Explanation
With unequal class widths, plot frequency densities.