Question

Makayla 在 $9$ 小时工作日中参加了两场会议。第一场会议用了 $45$ 分钟，第二场会议用时是第一场的两倍。她工作日的百分之多少用于参加会议？

Makayla attended two meetings during her $9$ -hour work day. The first meeting took $45$ minutes and the second meeting took twice as long. What percent of her work day was spent attending meetings?

$15$

$20$

$25$

$30$

$35$

答案：C

知识点：百分数单位换算

难度评级：870

小提示：

把会议时间换成相同单位。

Convert the meeting times to the same units

大提示：

两场会议共 $45+90$ 分钟，而工作日为 $9$ 小时。

The meetings last $45+90$ minutes out of $9$ hours

解答：

$45$ 分钟等于 $\dfrac{45}{60} = \dfrac{3}{4}$ 小时。第二场会议用时为 $2 \cdot \dfrac{3}{4} = \dfrac{3}{2}$ 小时，所以两场会议共用 $\dfrac{3}{4} + \dfrac{3}{2} = \dfrac{9}{4}$ 小时。这占整个工作日的 $100 \% \cdot \dfrac{\frac{9}{4}}{9} = 100 \% \cdot \dfrac{1}{4} = 25 \%\text{。}$

所以正确答案是 C。

Note that $45$ minutes is $\dfrac{45}{60} = \dfrac{3}{4}$ hours. The second meeting is then $2 \cdot \dfrac{3}{4} = \dfrac{3}{2}$ hours. Both meetings take a total of $\dfrac{3}{4} + \dfrac{3}{2} = \dfrac{9}{4}$ hours then. The percent of Makayla’s work day spent attending meetings is $100 \% \cdot \dfrac{\frac{9}{4}}{9} = 100 \% \cdot \dfrac{1}{4} = 25 \%.$

Thus, C is the correct answer.

2010 AMC 10B 第 2 题

答案：C

难度评级：870

小提示：

大提示：

解答：

其他年份的第 2 题