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.