7. You measure the lifetime of a random sample of 64 tires of a certain brand. I

Question

7. You measure the lifetime of a random sample of 64 tires of a certain brand. In a follow-up study, more tires were available for testing, so you were able to measure the lifetimes of a random sample of 100 tires rather than 64. Which statement is TRUE?

The margin of error for our 99% confidence interval would decrease.
The margin of error for our 99% confidence interval would increase.
The margin of error for our 99% confidence interval would stay the same because the level of confidence has not changed.
would decrease.

8.
A medical researcher treats 400 subjects with high cholesterol with a new drug. The average decrease in cholesterol level is = 90 after two months of taking the drug. Assume that the decrease in cholesterol after two months of taking the drug follows a Normal distribution, with unknown mean and standard deviation = 30.

A 95% confidence interval for is:

90 ± 1.96.
90 ± 2.94.
90 ± 3.92.
90 ± 58.8.

9. You plan to construct a confidence interval for the mean of a Normal population with (known) standard deviation . Which of the following will reduce the size of the margin of error?

Use a lower level of confidence.
All of the above
Reduce .
Increase the sample size.

10.
To assess the accuracy of a laboratory scale, a standard weight known to weigh 1 gram is repeatedly weighed a total of n times, and the mean of the weighings is computed. Suppose the scale readings are Normally distributed, with unknown mean m and standard deviation = 0.01 g. How large should n be, so that a 95% confidence interval for m has a margin of error of ± 0.0001?

38,416
10,000
100
196

Explanation / Answer

The solution for first question is given below. As per Chegg policy, only first question need to be answered, please repost the remaining questions.

As the sample size increases, the margin of error decreases, thus, The margin of error for our 99% confidence interval would decrease.

Thanks.

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