There are some so-called blackjack strategies out there that players no in the know will swear by. Assuming that the dealer has a card worth 10 for a hole card is one such strategy.
Sure on the surface it might sound like an okay strategy to use in blackjack, almost like it is a safety net based on the player assuming the worse. But the statistics do not add up on this one. And it is those statistics that show it as the bad blackjack strategy that it is.
To begin with, and to make the math simple at first, we are going to look at a single deck. In a single suit there are thirteen cards. All of those cards have their face value applied in blackjack except for the three face cards and the Ace which has the ability to be played as a 1 or an 11; the three face cards (Jack, Queen and King) are each worth 10. So out of thirteen cards in a single suit, only four (10, Jack, Queen and King) are worth 10; obviously the other nine cards are not worth 10.
So let’s break that down into percentages. Because there are only four cards in a suit worth 10, it means there is only a 30% chance of one being the hole card, and a 70% chance that the hole card will be a card that does not have a value of 10.
Even when you add more suits and in turn add more decks, the percentage of the hole card being worth 10 is still going to stick pretty close to 30%. So if the odds are in favor of the hole card being something other than a 10, why use a blackjack strategy that is based on poor odds? Because to me a 30% chance on the hole card being worth 10 is a pretty poor odds.
Considering that the odds are against the hole card being worth 10, it gives blackjack a house edge of 10.03 to assume the dealer’s hole card is worth 10. And that is an extremely bad house edge for blackjack. Never assume the dealer’s hole card is worth 10.