A random sample of 121 automobiles traveling on an interstate showed an average speed of 65 mph. From past information, it is known that the standard deviation of the population is 22 mph. The 95 percent confidence interval for μ is determined as (61.08, 68.92). If we are to reduce the sample size to 100 (other factors remain unchanged), the 95 percent confidence interval for μ would:
A) become wider.
B) become narrower.
C) be the same.
D) be impossible to determine.

Question

Quizplus · Accepted Answer

The width of the confidence interval is inversely related to the square root of the sample size (n). Reducing the sample size from 121 to 100 increases the standard error, making the confidence interval wider.

A Random Sample of 121 Automobiles Traveling on an Interstate