Question

学年开始时，Lisa 的目标是在全年 $50$ 次小测中至少 $80\%$ 得 A。前 $30$ 次小测中她有 $22$ 次得 A。若要达成目标，剩下的小测中她最多有多少次可以低于 A？

At the beginning of the school year, Lisa’s goal was to earn an A on at least $80\%$ of her $50$ quizzes for the year. She earned an A on $22$ of the first $30$ quizzes. If she is to achieve her goal, on at most how many of the remaining quizzes can she earn a grade lower than an A?

$1$

$2$

$3$

$4$

$5$

答案：B

知识点：百分数

难度评级：1050

小提示：

$50$ 次小测的 $80\%$ 是她需要得 A 的次数。

$80\%$ of $50$ quizzes is the number of A’s she needs

大提示：

剩下 $20$ 次中，她还需要 $40 - 22$ 次 A。

She needs $40 - 22$ more A’s out of the remaining $20$ quizzes

解答：

Lisa 至少需要 $0.8 \cdot 50 = 40$ 次 A。

她已经有 $22$ 次，所以剩下 $20$ 次中还需要 $40 - 22 = 18$ 次 A。

因此最多可以有 $20 - 18 = 2$ 次低于 A。

所以正确答案是 B。

Lisa needs an A on at least $0.8 \cdot 50 = 40$ quizzes.

She has $22$ already, so she needs $40 - 22 = 18$ more of the remaining $20$ quizzes.

She can earn a lower grade on at most $20 - 18 = 2$ of them.

Thus, the correct answer is B.

2005 AMC 12B 第 4 题

答案：B

难度评级：1050

小提示：

大提示：

解答：

其他年份的第 4 题