In the example from the web site I was trying out this problem in page 107 about Goodness of fit test for a normal distribution.Question is about analysis of fat content of hamburgers.
I understand that we need to have the two intervals -$\infty$< x< 26 and $40< x<$$\infty$ to find the class probabilities of intervals 26< x <28 and
But why should the expected frequencies of the two intervals -$\infty$< x< 26 and $40< x<$$\infty$ be also calculated and used for chi Squared value. These two categories are not there in the given data set.
Is it necessary to break our intervals such that they start from -infinity and end from infinity as this is a normal distribution?