two to come odds

Why are there different percentage figures on pages 105 and 112 within Petriv's odds book. By this I mean, why is it on page 105 it is approximately 31 and 35 % for 9 outs and on page 112 it is listed as 19 and 20% for the same 9 outs with two to come? The two tables contradict one another; but I'm sure there's a good explanation out there. It would seem the 19 and 20 % is more acurate, but the 31 and 35% is more widely used in other books.

Anyone know how to give a layman's explanation on this one?

Thanks in advance.