一个小组里有 12 名女生 and 9 名男生。

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 probability of selecting a boy and simplify it.

Total number of people $=12+9=21$ .

Number of boys $=9$ .

$P(\text{boy})=\frac{9}{21}=\frac{3}{7}$

答案

$\dfrac{3}{7}$

1. Let the number of more boys needed be $x$ and form the probability equation.

Let $x$ be the number of more boys needed.

Then the number of boys becomes $9+x$ , and the total number of people becomes $12+9+x=21+x$ .

$\frac{9+x}{21+x}=\frac{4}{5}$

2. Solve the equation for $x$.

$5(9+x)=4(21+x)$
$45+5x=84+4x$
$x=39$

答案

$51$ boys

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。