Question

Colfax Middle School 有 $270$ 名学生，男生与女生的比为 $5 : 4$ 。Winthrop Middle School 有 $180$ 名学生，男生与女生的比为 $4 : 5$ 。两所学校举办舞会，所有学生都参加。舞会上女生占学生总数的几分之几？

There are $270$ students at Colfax Middle School, where the ratio of boys to girls is $5 : 4.$ There are $180$ students at Winthrop Middle School, where the ratio of boys to girls is $4 : 5.$ The two schools hold a dance and all students from both schools attend. What fraction of the students at the dance are girls?

$\dfrac{7}{18}$

$\dfrac{7}{15}$

$\dfrac{22}{45}$

$\dfrac{1}{2}$

$\dfrac{23}{45}$

答案：C

知识点：比与比例分数

难度评级：1140

解答：

女生总数为 $\dfrac{4}{9} \cdot 270 + \dfrac{5}{9} \cdot 180 =$ $120 + 100 = 220.$

学生总数为 $270 + 180 = 450$ ，所以女生所占比例为 $\dfrac{220}{450} = \dfrac{22}{45}$ 。

所以正确答案是 C。

The total number of girls is $\dfrac{4}{9} \cdot 270 + \dfrac{5}{9} \cdot 180 =$ $120 + 100 = 220.$

There are $270 + 180 = 450$ students total, so the fraction of girls is $\dfrac{220}{450} = \dfrac{22}{45}.$

Thus, C is the correct answer.

2011 AMC 8 第 14 题

答案：C

难度评级：1140

解答：

其他年份的第 14 题