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.

Answer 1

Answer:

b. The engineer who weighed the rod 25 times.

Step-by-step explanation:

Hello!

Full text:

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.

Suppose the engineers construct a 90% confidence interval for the true length of their rods. Whose interval do you expect to be more precise (narrower)?

a. Both confidence intervals would be equally precise.

b. The engineer who weighed the rod 25 times.

c. The engineer who weighed the rod 20 times.

X₁: Length of an eastern rod of the Bay Bridge

n₁= 25

X₂: Length of a western rod of the Bay Bridge

n₂= 20

Both Engineers will use their samples to estimate the population average length of the rods using a 90% CI.

Assuming the standard normal distribution, the confidence interval will be centered in the estimated mean.

X[bar] ± $Z_{1-\alpha /2}$*(σ/√n)

And the width is determined by the semi amplitude:

↓d= $Z_{1-\alpha /2}$*(σ/√↑n)

As you can see the sample size has an indirect relationship with the semi amplitude of the interval. This means, when the sample size increases, the semi amplitude decreases, and if the sample size decreases, the semi amplitude increases. Naturally this is leaving all other elements of the equation constant, this means, using the same confidence level and the same population standard deviation.

Since the first engineer took the larger sample, he's confidence interval will be narrower and more accurate.

Hope this helps!