I'm quite sure that the only reason your answers are "off by a little bit" is that you have used the numbers from the tables, and they are only accurate to a limited number of significant figures. (How do I know this is the reason? Because the numbers in the tables have no more than 5 significant figures, while the answers (except b) have a lot more).
The only way to get more accurate answers would be to recreate the tables in Excel or R, with a greater degree of precision, and do your calculations from there.
On page xix of the book, the authors confirm this: "In the worked examples in the text, we have worked with greater accuracy than we record, so there will be some differences from rounding when working with intermediate figures."