Multi-Deck Blackjack Strategy
One simple way to look at it is to play as if the dealer's facedown card is a 10. Since 10-value cards (10, jack, queen, king) comprise four of the 13 denominations in the deck, that is the single most likely value of any unseen card. Therefore, if you have 16 and the dealer's up-card is a 7, you are guessing that the most likely dealer total is 17. The dealer would stand on 17 to beat your 16; therefore, you must hit the 16 to have the best chance to win.