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Records show that the distance driven by a bus driver in a week is normally distributed with mean $1150{\text{ }}km$ and standard deviation $105{\text{ }}km$. New driving regulations are introduced and in the next 20 weeks he drives a total of $21800{\text{ }}km$.

a) Stating any assumption(s), test, at the 1% significance level, whether his mean weekly driving distance has decreased.

b) A similar test at the 1% significance level was carried out using the data from another 20 weeks. State the probability of a Type I error and describe what is meant by a Type I error in this context.

پاسخ تشریحی :
نمایش پاسخ

a) Assume pop sd same (105)

${H_0}:Pop{\text{ }}mean = 1150$

${H_1}:Pop{\text{ }}mean \lt 1150$

$\frac{{\frac{{21800}}{{20}} - 1150}}{{\frac{{105}}{{\sqrt {20} }}}}$

$ =  \pm 2.556$ or $2.56$

Compare with $z =  \pm 2.326$

(for a clear 2 tail test compare with $ \pm 2.576$)

Evidence that mean distance decreased

b) $0.01$

Concluding there has been a decrease when there has not.

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