Question 905:

Asked on December 3, 2011

Tags: Confidence Intervals

1

Answer:

No answer provided yet.First we need to calculate the standard error of the mean which is the standard deviation divided by the square root of the sample size: 4/SQRT(20) = .8944

Next we find the margin of error which is the standard error times the critical value from the t-distribution for a 95% level of confidence. We look this value up in a t-table or use the excel function = TINV(.05,19) where the values are alpha (1-.95) and the degrees of freedom (sample size -1). This gets us a value of 2.09. So the margin of error is .8944*2.09 = 1.872.

Finally we add and subtract the margin of errors to the sample mean: 55-1.872 and 55+1.872 and we get the 95% confidence interval of 53.13 to 56.87.