Question

Previous scenario: A random sample of 121 motorcycles on highway 111 showed an average speed of 65 mph. It is known that the standard deviation of all motorcycle speeds is 22 mph. New question: If the confidence level were changed from 96.6% as it was in the previous question to 90%, the margin of error

will increase

will decrease

remains unchanged

becomes negative

** the answer is not will increase

Answer 1

Sample size is large. So this is a z-test problem.

Margin of error = se() *

When confidence = 96.6%, = 0.034, So, = 2.12

When confidence = 90%, = 0.1, So, = 1.645

se() is same for both the cases. But, as for 90% confidence is smaller than for 96.6% confidence. So, If the confidence level were changed from 96.6% as it was in the previous question to 90%, the margin of error will decrease.

**If this answers do not match or any kind of confusion you have please comment