Question 908:

Asked on December 3, 2011

Tags: 1-sample t-test

1

Answer:

No answer provided yet.First we need to calculate the standard error of the mean (SEM) which is the standard deviation divided by the square root of the sample size: 5/SQRT(40) = .7905

Next we find the margin of error which is the standard error times the critical value from the t-distribution for a 90% level of confidence. We look this value up in a t-table or use the excel function = TINV(.10,39) where the values are alpha (1-.90) and the degrees of freedom (sample size -1). This gets us a value of 1.68. So the margin of error is .7905*1.68 = 1.33.

Finally we add and subtract the margin of errors to the sample mean: 65-1.68 and 65+1.68 and we get the 90% confidence interval of 63.67 to 66.33.