Posted by **sue** on Monday, December 19, 2011 at 2:39pm.

In Dallas, some fire trucks were painted yellow (instead of red) to heighten their visibility. During a test period, the fleet of red fire trucks made 153,348 runs and had 20 accidents, while the fleet of yellow fire trucks made 135,035 runs and had 4 accidents. At α = .01, did the yellow fire trucks have a significantly lower accident rate? (a) State the hypotheses. (b) State the decision rule and sketch it. (c) Find the sample proportions and z test statistic. (d) Make a decision. (e) Find the p-value and interpret it. (f ) If statistically significant, do you think the difference is large enough to be important? If so, to whom, and why? (g) Is the normality assumption fulfilled? Explain.

Accident Rate for Dallas Fire Trucks

Statistic Red Fire Trucks Yellow Fire Trucks

Number of accidents x1 = 20 accidents x2 = 4 accidents

Number of fire runs n1 = 153,348 runs n2 = 135,035 runs

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