Question

In order to set reasonable fund-raising targets, a charitable organization wishes to know the average monthly income of their members. National data suggest incomes should be normally distributed with a standard deviation of σ=221 dollars. If 91 members are randomly selected and their average monthly income found to be x ¯ = 2270 dollars, find the following. Round your answers to two decimal places.

a) The critical value at the 90% confidence level is zcrit = _______

b) A 90% confidence interval for the average salary of the membership, assuming that it is large.  ______ ≤ μ ≤ ______

c) A 90% confidence interval for the average salary of the membership if the total membership is N=1464. ______ ≤ μ ≤ ______  

Answer 1