# Thread: confidence integral and true proportion....

1. ## confidence integral and true proportion....

I keep coming up with the same answer and my software says I am wrong... Hopefully you will come up with a different one or help me out how to figure it out...
THANKS!

A university is interested in evaluating registration processes. Students can either register for classes by using either a telephone registration system (Group 1) or an online system that is accessed through the university's web site (Group 2).

Independent random samples of 95 students who registered by phone and 60 students who registered online were selected. Of those who registered by phone, 57 reported that they were satisfied with the registration process. Of those who registered online, half of them reported that they were satisfied.

According to the results, rounded to the nearest percent, the university is 95% confident that the true proportion difference in the two groups that are satisfied with the registration process is between % and %.

2. What did you get?

3. -6.03 % and 26.03 %

I put it into my calculator 2-PropZint and plugged in all the figures but that isn’t right so I tried to do it on paper with the Z-score test but none of my notes include 2 propositions.

$p_1 = \frac{57}{95 }, p_2 = \frac{30}{60 }, n_1 = 95, n_2 = 60$
$Z_{0.95}= 1.96$
C.I = $p_1-p_2 \pm Z_{0.95}\times \sqrt{\frac{p_1(1-p_1)}{n_1}+\frac{p_2(1-p_2)}{n_2}}$