You're dealt a pair of 10s. The dealer shows a 9. Split or play it as one hand? Basic strategy answers:
| Stand ← | +0.7584 |
| Split | +0.2331 |
| Hit | -0.8508 |
| Double | -1.7017 |
| You bust on the next card | 92.3% |
| Dealer 9 busts | 22.8% |
Stand is not close: it beats Split by 0.5253 per unit. Getting this one wrong costs $5.25 on a $10 bet, every single time. It is also the 8th best spot you can be in out of the 340 hands in this chart. Expected value is per unit staked, computed for multi-deck, dealer stands on soft 17, double after split allowed. The model and the code are published as data.
Two ten-value cards make 20 — the second-best hand possible. Splitting trades one near-certain winner for two uncertain hands. Against a 9, keeping the 20 wins about twice as often as each split hand would. Never split 10s. Yes, even when the dealer shows a 6.