2005 AMC 10B 第 6 题

Question

学年开始时，Lisa 的目标是在全年

50

次小测中至少

80\%

拿到 A。前

30

次小测中，她有

22

次拿到 A。若她要达成目标，剩余小测中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：百分数不等式

难度评级：960

小提示：

先求她总共需要多少个 A。

Find how many A’s she needs in total

大提示：

她需要

0.8\cdot50

个 A，而还剩

20

次小测。

She needs

0.8\cdot50

A’s, and

20

quizzes remain

解答：

Lisa 至少需要

0.8 \cdot 50 = 40

次小测拿到 A。

她已经有

22

个 A，所以剩下

20

次中还需要

40 - 22 = 18

个 A。

因此最多有

20 - 18 = 2

次小测低于 A。

所以正确答案是 B。

Lisa needs an A on at least

0.8 \cdot 50 = 40

quizzes.

She already has

22,

so she needs

40 - 22 = 18

A’s among the remaining

20

quizzes.

That leaves at most

20 - 18 = 2

quizzes with a grade lower than an A.

Thus, B is the correct answer.

2005 AMC 10B 第 6 题

答案：B

难度评级：960

小提示：

大提示：

解答：

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