Blackjack Strategy When Splitting a Pair of Nines
Split: When the dealer has 2-6 and 8-9.
Stand: When the dealer has a 7, 10 or Ace.
Why to split a pair of nines
This seems to be one of the most confusing and complicated strategy in blackjack, but it really isn't. First of all, a pair of nines adds up to 18, which is a decent hand. Mathematically, your overall odds in the long term are better by taking advantage of a split and hopefully get two 19's. This strategy depends very closely on what the dealer is holding though. The 2 thru 6 dealer upcard strategy is simple: you are hoping for the dealer to bust by getting a run of ten cards.
If the dealer is holding an 8 or 9, he must stand on 18 or 19 if a ten is drawn. Luckily if you get two hands of 19, you can beat his 18 or tie his 19. The odds say that a split is the most optimal choice over the long time duration.
Why to stand on a pair of nines
If the dealer has a 10 or Ace card showing, then it makes sense to just stand on 18 and not risk betting more money on a split that has a high probability of losing if the dealer gets a 20 or 21.
It is not as obvious as to why you should stand when the dealer has a 7 showing. The strategy really isn't that complicated though. If you stand with a pair of nines, your total hand will be 18. If the dealer hits and draws a ten, he will have to stand on 17, so you automatically win. The reason you shouldn't split is you still have to assume that you need to beat the 17 on both hands and the dealer has to stand on 17, meaning he don't be going bust anytime soon. The odds say that if you split, you will likely lose a lot more money than if you were to just stand on 18.