In the book Probability and Statisitics for Engineering and the Sciences, chapter 3 problem 54 b, they do some work which I understand and they come up with (4.45, 7.549). Then they say the answer is F(7) - F(4) and pull some answer out of no where.
Where is F(7) and F(4) coming from? There is a section in the book with tables and whatnot to convert things like this but I'm not seeing anything related to this in there.