Thirty daily index readings are 22,28,35,40,45,48,52,58,61,65,70,74,78,80,84,90,96,102,110,118,125,132,140,148,155,160,168,175,184,195.
Using classes \(0<x\le40,40<x\le80\), and so on to 200, construct a frequency table.
Draw a histogram.
Explain why a stem-and-leaf diagram is less suitable.
Values above 80 are unhealthy; find the percentage of unhealthy days.
July’s mean was 72. Assess whether air quality improved.
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Answer:(i) \(4,10,6,6,4\); (ii) corresponding histogram; (iii) less compact for grouped range comparison; (iv) \(53.3\%\); (v) improvement is suggested because \(72<97.9\), but the mean alone does not determine July’s unhealthy-day percentage.