下表显示了 200 人在游戏中所拿画笔的颜色。

它不会直接告诉你答案，而是问你卡在哪一步看看 AI 是怎么陪你一步步弄懂这道题的

完整解法

1. Find the total number of people who took a black pen.

Number who took black pens
$=15+23=38$

2. Convert the probability into a percentage.

Total number of people $=200$ .

Probability as a percentage
$=\frac{38}{200}\times 100\%=19\%$

答案

$19\%$

1. Identify the number of girls who took red pens and set up the probability for two selections without replacement.

From the table, the number of girls who took red pens is $5$ .

Since two persons are selected at random without replacement,
$P(\text{both are girls who took red pens})=\frac{5}{200}\times\frac{4}{199}.$

2. Calculate and simplify the probability to lowest terms.

$\frac{5}{200}\times\frac{4}{199}=\frac{20}{39800}=\frac{1}{1990}.$

Correction: since $200 \times 199 = 39800$ , and $5 \times 4 = 20$ ,
$\frac{20}{39800}=\frac{1}{1990}.$

答案

$\dfrac{1}{1580}$

AI 分析，可能出错

用 AI 批改，圈出写错的那一步，并自动将你的薄弱点存入错题本，形成你的错因库。