A college has decided to add support courses to its statistics classes to assist students. We look at the next semester to determine if the addition of the support courses assisted students. In a sample of 4 courses with support courses the average final grade of 160 students was 78% with a standard deviation of 2%. Calculate a 95% confidence interval for the population mean of students who took a support course. (Type numbers in Excel calculator without percent sign) O (77.69, 78.31) O (77.70, 78.30) O (77.69, 78. 30) (77.68, 78.31) 4 is not larger than 40 so we cannot compute a confidence interval.

An agriculture researcher plants twenty five plots with a new variety of corn. The average yielded for these plots is x-bar = 150 bushels per acre. Assume that the yield per acre for the new variety of corn follows a normal distribution with unknown mean and standard deviation = 10 bushels per acre. A 90% Confidence interval for mean is?

A forestry researcher is conducting a study of trees in the upper midwest. He selects a random sample of 125 red maple trees and measures the trunk diameter of each. The mean of the sample is 25 inches with a standard deviation of 5.2 inches, use this to find a 95% confidence interval for the mean trunk diameter of all red maple trees.

Tina catches a 14-pound bass.  She does not know the population mean or standard deviation.  So she takes a sample of five friends and they say the last bass they caught was 9, 12, 13, 10, and 10 pounds.  Find the t and calculate a 95% (α = .05) confidence interval.

A random sample of 500 observations yields x̅ =400 and s=50. What is the  95% confidence interval for the population mean?

You would like to estimate the variance of sick days at a Fortune 500 company.  You randomly select 15 employees and record how many sick days they have used in the past year and you get a sample standard deviation of 1.2.  Provide a 95% confidence interval estimate of the population variance.

A certain test preparation course is designed to help students improve their scores on the LSAT exam. A mock exam is given at the beginning and end of the course to determine the effectiveness of the course. The following measurements are the net change in 33 students' scores on the exam after completing the course: −6,11,18−6,11,18 Using these data, construct a 90%90% confidence interval for the average net change in a student's score after completing the course. Assume the population is approximately normal. Copy Data Step 4 of 4 :   Construct the 90%90% confidence interval. Round your answer to one decimal place.