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# Z-test for accident rates

In Dallas some fire trucks were painted yellow. During the test period, the fleet of red fire trucks made 153,348 runs and had 20 accidents. the fleet of yellow trucks made 135,035 runs and had 4 accidents. At a=.01, did the yellow fire trucks have a significantly lower accident rate?

Zc=2.326
Z=2.961
p-value=.0015
normality not justified

State null and alternative hypothesis.
Select a level of significance.
Identify the test statistics (give formula).
Formulate a decision rule.
Make a decision (compute sample proportions and Z statistic).
Compute p-value and interpret it.
Is the normality assumption fulfilled? Explain.

#### Solution Preview

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 ...

#### Solution Summary

Z-test for accident rates of a yellow fire truck is determined. A hypothesis test is used.

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