**Question**

Suppose the germination periods, in days, for grass seed are normally distributed. If the population standard deviation is 3 days, what minimum sample size is needed to be 90% confident that the sample mean is within 1 day of the true population mean?

Use the table above for the z-score, and be sure to round up to the nearest integer.

**Question**

The length, in words, of the essays written for a contest are normally distributed with a population standard deviation of 442 words and an unknown population mean. If a random sample of 24 essays is taken and results in a sample mean of 1330 words, find a 99% confidence interval for the population mean.

You may use a calculator or the common z values above.

**Question**

Suppose the scores of a standardized test are normally distributed. If the population standard deviation is 2 points, what minimum sample size is needed to be 90% confident that the sample mean is within 1 point of the true population mean?

Use the table above for the z-score, and be sure to round up to the nearest integer.

**Question**

The lengths, in inches, of adult corn snakes are normally distributed with a population standard deviation of 8 inches and an unknown population mean. A random sample of 25 snakes is taken and results in a sample mean of 58 inches.

Identify the parameters needed to calculate a confidence interval at the 99% confidence level. Then find the confidence interval.

You may use a calculator or the common z values above.

**Question**

The lengths, in inches, of adult corn snakes are normally distributed with a population standard deviation of 8 inches and an unknown population mean. A random sample of 25 snakes is taken and results in a sample mean of 58 inches.

What is the correct interpretation of the confidence interval?

Select the correct answer below:

- We can estimate with 99% confidence that the true population mean length of adult corn snakes is between 53.88 and 62.12 inches.
- We can estimate with 99% confidence that the sample mean length of adult corn snakes is between 53.88 and 62.12 inches.
- We can estimate that 99% of adult corn snakes will have a length that is between 53.88 and 62.12 inches

**Question**

The weights, in pounds, of dogs in a city are normally distributed with a population standard deviation of 2 pounds and an unknown population mean. A random sample of 16 dogs is taken and results in a sample mean of 28 pounds.

Identify the parameters needed to calculate a confidence interval at the 90% confidence level. Then find the confidence interval.

You may use a calculator or the common z values above.

**Question**

The weights, in pounds, of dogs in a city are normally distributed with a population standard deviation of 2 pounds and an unknown population mean. A random sample of 16 dogs is taken and results in a sample mean of 28 pounds.

What is the correct interpretation of the confidence interval?

Select the correct answer below:

- We can estimate that 90% of the dogs in the city have a weight that lies between 27.18 and 28.82 pounds.
- We can estimate with 90% confidence that the sample mean weight of dogs in the city is between 27.18 and 28.82 pounds.
- We can estimate with 90% confidence that the true population mean weight of dogs in the city is between 27.18 and 28.82 pounds.

**Question**

Suppose the heights of seasonal pine saplings are normally distributed. If the population standard deviation is 14 millimeters, what minimum sample size is needed to be 95% confident that the sample mean is within 4 millimeters of the true population mean?

Use the table above for the z-score, and be sure to round up to the nearest integer.

**Question**

The population standard deviation for the scores of a standardized test is 4 points. If we want to be 90% confident that the sample mean is within 1 point of the true population mean, what is the minimum sample size that should be taken?

Use the table above for the z-score, and be sure to round up to the nearest integer.

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