Length of a rod: Engineers on the Bay Bridge are measuring tower rods to find ou
ID: 3249372 • Letter: L
Question
Length of a rod: Engineers on the Bay Bridge are measuring tower rods to find out if any rods have been corroded from salt water. There are rods on the east and west sides of the bridge span. One engineer plans to measure the length of an eastern rod 25 times and then calculate the average of the 25 measurements to estimate the true length of the eastern rod. A different engineer plans to measure the length of a western rod 20 times and then calculate the average of the 20 measurements to estimate the true length of the western rod.
The engineer who collected 20 measurements for the western rod uses the mean to calculate the 90% confidence interval for rod length (in feet). Her interval is (23.76, 24.23). What does a 90% confidence interval tell you about rod length in this case?
A) The engineer is 90% confident that the true length of the rod is between 23.76 feet and 24.23 feet.
B)The engineer is 90% confident that most rods of this type have lengths between 23.76 feet and 24.23 feet.
C) The engineer is 90% confident that this interval includes the mean of the 20 length measurements she took.
Weight of a rock: In a geology course, students are learning to use a balance scale to accurately weigh rocks. One student plans to weigh a rock 20 times and then calculate the average of the 20 measurements to estimate her rock's true weight. A second student plans to weigh a rock 5 times and calculate the average of the 5 measurements to estimate his rock's true weight.
Which student is more likely to come the closest to the true weight of the rock he or she is weighing?
A)The student who weighed the rock 20 times.
B)The student who weighed the rock 5 times.
C)Both averages would be equally close to the true weight.
Explanation / Answer
Length of the rod:
90% confidence interval tells:
The engineer is 90% confident that the true length of the rod is between 23.76 feet and 24.23 feet.
Option A is correct.
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