Question

从一副牌中发出两张牌。这副牌有四张红牌，分别标为 $A$ 、 $B$ 、 $C$ 、 $D$ ，还有四张绿牌，也分别标为 $A$ 、 $B$ 、 $C$ 、 $D$ 。一对获胜牌是两张同色牌或两张同字母牌。抽到一对获胜牌的概率是多少？

Two cards are dealt from a deck of four red cards labeled $A,$ $B,$ $C,$ $D$ and four green cards labeled $A,$ $B,$ $C,$ $D.$ A winning pair is two of the same color or two of the same letter. What is the probability of drawing a winning pair?

$\dfrac{2}{7}$

$\dfrac{3}{8}$

$\dfrac{1}{2}$

$\dfrac{4}{7}$

$\dfrac{5}{8}$

答案：D

知识点：基本概率无放回抽样

难度评级：1450

解答：

抽出第一张牌后，还剩 $7$ 张。其中 $3$ 张同色， $1$ 张同字母。因此在这 $7$ 张牌中有 $4$ 张会形成获胜牌对。

概率为 $\dfrac{4}{7}$ 。

所以正确答案是 D。

After drawing the first card, there are $7$ left. $3$ of them have the same color, and $1$ of them has the same letter. Therefore, there are $4$ out of $7$ possibilities that result in a winning pair.

The probability of drawing a pair is then $\dfrac{4}{7}.$

Thus, D is the correct answer.

2007 AMC 8 第 21 题

答案：D

难度评级：1450

解答：

其他年份的第 21 题