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.

This may be a case of the blind leading the blind as I am just learning this. But look at page 48 which uses combinations to get odds for a flush draw(9 outs)with two to come.The odds of making a flush by the river on the flop are 1.85 to 1 ( rounded to 1.9 in the table on page 105)The odds against making a flush draw on the river, given that you have missed it on the turn, are 46-9:9 or 4.1:1 which is the same as the table on page 112. Steve

The way you calculate odds of outs with 2 cards to come is to calculate the odds of not making your outs. With 47 cards in play, and 9 outs, there are 38 bad cards. The chance of the turn being bad is 38/47. The chance of the river being bad, given the turn was bad, is 37/46. Take the product, and get 65%. Take this from one, and the probability of getting at least one of your outs is 35%. With 45 cards in play, and 9 outs, the probability goes slightly up to 36.4%. I have no idea where the 31% came from.