Use the following information for Questions 5-7

A contractor involved in high-rise building construction orders thousands of steel rods each year from a supplier. The strength, X, of the rods is a normally distributed random variable. When a shipment arrives, the contractor selects a random sample of 15 rods and determines the sample mean strength and the sample standard deviation. These results are then used to compute a confidence interval for the population mean strength of the rods.

5. For a particular shipment, the sample mean strength of the selected rods is x = 990 pounds and the sample standard deviation is s = 14.5 pounds. What is the margin of error for a 95% confidence interval for the population mean strength? (Round your answer to 2 decimal places.)

1. a)8.03 lbs
2. b)7.98 lbs
3. c)7.34 lbs
4. d)8.31 lbs
5. e)None of the above

6. The contractor would like to have an interval that has a smaller margin of error than the one above. Which of the following would contribute to accomplishing this goal? (Choose the most appropriate response.)

1. a)Both decreasing the size of the sample mean strength and increasing the size of the sample to 30 rods would contribute to a reduction in the margin of error.
2. b)Decrease the size of the sample mean strength.
3. c)Increase the size of the sample to 30 rods.
4. d)Increase the level of confidence to 99%
5. e)None of the above

7.

tires. It wishes to develop a confidence interval estimate that would have a margin of error less than 400 miles with 99 percent confidence. Suppose the population standard deviation is equal to 4,000 miles. Based on this information, the required sample size should be at least:

1. a)542
2. b)543
3. c)663
4. d)664
5. none of the above