Real Challenge 4.4.3.

When two cards are drawn from a usual deck of 52 poker cards, what isthe probability of getting a "blackjack"? (That is, an ace togetherwith a K, Q, J or 10)
SOL
分母=C(52,5)=52!/(5!*47!)=52*51*10*49*2
分子=C(4,1)*C(4,1)*C(4,1)*C(4,1)*C(4,1)=4^5
P=分子/分母
=4^5/(52*51*10*49*2)
=64/162435

Answer:

Required probability

= 4C1 * (4*4C1) / 52C2

= 32/663