In order to express the confidence interval in the form p ± E, first we have to determine the midpoint of the interval, like this:
[tex]\hat{p}=\frac{0.555+0.999}{2}=0.777[/tex]
The value of the error, E, can be calculated by taking the difference between p and the end of the interval, like this:
[tex]E=0.999-0.777=0.222[/tex]
Then, we can express 0.555 < p < 0.999 in p + E notation as 0.777 ± 0.222
