MATHEMATICS

4.26 Find the sample mean. You are given the following hypotheses:

We know that the sample standard deviation is 10 and the sample size is 65. For what sample

mean would the p-value be equal to 0.05? Assume that all conditions necessary for inference are

satisfied.

 

4.28 Testing for food safety. A food safety inspector is called upon to investigate a restaurant with a few customer reports of poor sanitation practices. The food safety inspector uses a hypothesis testing framework to evaluate whether regulations are not being met. If he decides the restaurant is in gross violation, its license to serve food will be revoked.

(a) Write the hypotheses in words.

(b) What is a Type 1 error in this context?

(c) What is a Type 2 error in this context?

(d) Which error is more problematic for the restaurant owner? Why?

(e) Which error is more problematic for the diners? Why?

(f) As a diner, would you prefer that the food safety inspector requires strong evidence or very

strong evidence of health concerns before revoking a restaurant’s license? Explain your reasoning.

 

4.30 Car insurance savings, Part I. A car insurance company advertises that customers switching to their insurance save, on average, $432 on their yearly premiums. A market researcher at a competing insurance discounter is interested in showing that this value is an overestimate

so he can provide evidence to government regulators that the company is falsely advertising their

prices. He randomly samples 82 customers who recently switched to this insurance and finds an

average savings of $395, with a standard deviation of $102.

(a) Are conditions for inference satisfied?

(b) Perform a hypothesis test and state your conclusion.

(c) Do you agree with the market researcher that the amount of savings advertised is an overestimate? Explain your reasoning.

(d) Calculate a 90% confidence interval for the average amount of savings of all customers who

switch their insurance.

(e) Do your results from the hypothesis test and the confidence interval agree? Explain.

 

 

4.32 Speed reading, Part I. A company offering online speed reading courses claims that students who take their courses show a 5 times (500%) increase in the number of words they can read in a minute without losing comprehension. A random sample of 100 students yielded an average increase of 415% with a standard deviation of 220%. Is there evidence that the company’s claim is false?

(a) Are conditions for inference satisfied?

(b) Perform a hypothesis test evaluating if the company’s claim is reasonable or if the true average improvement is less than 500%. Make sure to interpret your response in context of the hypothesis test and the data. Use α= 0:025.

(c) Calculate a 95% confidence interval for the average increase in the number of words students

can read in a minute without losing comprehension.

(d) Do your results from the hypothesis test and the confidence interval agree? Explain.

 

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