When to Split 10s

In an upcoming post on Huffington Post, I compare the business decisions of companies like Microsoft, Google and Facebook with those that I made at the blackjack table. Specifically, I talk about the difficulty of splitting 10s.

Here’s the passage from my book, “The House Advantage” where I discuss when and why you split 10s.

The math behind splitting 10s is relatively simple. With a 20 against a dealer’s 6, you have roughly an 85 percent chance to win the hand. So your expected value is 0.70 (0.85-0.15) times whatever you have bet, in this case $8,000. My expected value of standing on the 20 was $5,600.

If you split the 10s, putting another $8,000 down on the table, your new expected value is the sum of the expected value of each new hand. Starting with a 10 against the dealer’s 6, you will win roughly 64 percent of the time. So in this case your expected value is simply .28 (.64-.36) times $16,000 (the sum of the two bets). My expected value of splitting the 10s was $4,480.

These numbers apply to normal conditions, facing a deck with a standard ratio of high cards to low cards remaining. However, when the deck gets rich in high cards, your odds of winning in each scenario–splitting versus standing–both increase. And the more the deck gets skewed toward high cards remaining the more the probability of winning in each scenario increases.

Let’s take the extreme case when you know there are only high cards remaining in the deck. If you stand your 20 you will have pretty close to a 100 percent chance to win and your expected value will be $8,000. But if you split your 10s you will also have close to a 100 percent chance to win and your expected value will be close to $16,000, two times your expected value for standing.

Of course this is merely a theoretical ideal scenario but it illustrates the value of splitting 10s. In a favorable situation it allows you to put more money on the table and therefore win more money.

Splitting 10s is something called a “numbers play” and is something you only do once you have mastered all other aspects of card counting. Numbers plays are deviations to basic strategy based on the count at your table.


One Comment on “When to Split 10s

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