The length, in words, of the essays written for a contest are normally distributed with a population standard deviation of 442 words and an unknown population mean. if a random sample of 24 essays is taken and results in a sample mean of 1330 words, find a 99% confidence interval for the population mean.

Step-by-step explanation:

Given : Level of significance :

Then , significance level :

Since , sample size : , which is small sample (n<30) so the test applied here is a t-test.

Degree of freedom=

Using t-distribution table , Critical value :

Sample mean :

Standard deviation:

The confidence interval for population mean is given by :-

Hence,  a  99% confidence interval for the population mean.=

answer: the answer is 35%

b.an increase in a causes b to decrease