Question

7. License Plate Laws The Chapter Problem involved passenger cars in Connecticut and passenger cars in New York, but here we consider passenger cars and commercial trucks. Among 2049 Connecticut passenger cars, 239 had only rear license plates. Among 334 Connecticut trucks, 45 had only rear license plates (based on samples collected by the author). A reasonable hypothesis is that passenger car owners violate license plate laws at a higher rate than owners of commercial trucks. Use a 0.05 significance level to test that hypothesis. a. Test the claim using a hypothesis test. b. Test the claim by constructing an appropriate confidence interval

Answer 1

Yes it is true that commercial truck owners violate laws requiring front license plates at a higher rate than owners of passenger cars because null hypothesis is rejected.

Given among 2049 Connecticut passenger cars, 239 had only rear license plates. Among 334 Connecticut trucks, 45 had only rear license plates.

let $p_{1}$ be the probability that commercial cars have rear license plates and $p_{2}$ be the probability that connected trucks have rear license plates.

                         Cars                     Trucks                         Total

Total                  2049                    334                             2383

x                          239                      45                                284

p                        0.1166                   0.1347                          0.1191

α=0.05

Hypothesis will be  :

$H_{0}:p_{1} =p_{2}$

$H_{1} :p_{1} < p_{2}$

It is a left tailed test at 0.05 significance.

Standard errors of p=$\sqrt{p(1-p)/n}$

=$\sqrt{(0.1191*0.8809)/2383}$

=$\sqrt{0.1049/2383}$        

=0.0066

Test statistic Z=p difference/standard error

=(0.1166-0.1347)/0.0066

=-0.0181/0.0061

=-2.967

p value=0.001505<5%

Since p is less than 5% we reject null hypothesis.

We cannot calculate standard deviation so  we cannot calculate confidence interval.

Hence there is statistical evidence at 5% significance level to support that commercial truck owners violate laws requiring front license plates at a higher rate than owners of passenger cars.

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