In blackjack, the probability of the dealer busting depends on the card the dealer shows, known as the "upcard." On average, the dealer busts about 28% of the time across all possible upcards.

To estimate how often the dealer busts in 20 hands, we can multiply the average bust rate by the number of hands:

Expected busts = 20 × 0.28 = 5.6

So, in 20 hands, the dealer is likely to bust approximately 5 to 6 times on average. However, this can vary depending on the specific upcards and the game’s rules.