probability

That's damn difficult..................

In order to get blackjack, as the question metioned, an ace together with a K, Q, J or 10). There are only 2 cards. However, 3 or more cards can add up to 21 (blackjack).

2 cards:

First card Second card
A K,Q,J,10

=4/52*16/51 = 0.02413273

First card Sceond
K,Q,J,10 A

=16/52*4/51 = 0.02413273

Total probility for 2 cards = 0.04826546 or 4.8 %

3 cards ..........as the question assume only 2 cards, i don't show working here.
3 cards or more for example, you get 5, 6, and 10 = 21. or 4 cards, 4, 5, 3, 9 =21 . The more the no. of cards are, the more steps of calculation.

2009-11-18 21:37:25 補充：
he didn't, you may get K,Q,J,10 first , A second. So there are 2 situation.

Yes I forget to multiply two for Ace + Ten & Ten + Ace.

nelsonywm2000 sir :

你是否沒有乘2 ?