2011 AMC 12B 第 2 题

Question

Josanna 到目前为止的考试成绩是

90

，

80

，

70

，

60

，和

85

。她的目标是在下一次考试后，把平均分至少提高

3

分。她下一次考试至少需要多少分才能达到目标？

Josanna’s test scores to date are

90,

80,

70,

60,

and

85.

Her goal is to raise her test average at least

3

points with her next test. What is the minimum test score she would need to accomplish this goal?

80

82

85

90

95

知识点：平均数

先求前五次考试的当前平均分。

Find the current average of the five scores

六次考试的总分必须等于目标平均分的

6

倍。

The six scores must total

6

times the target average

前五次总分为

90+80+70+60+85=385

，平均分为

77

。目标是新的平均分至少为

80

。

六次考试平均

80

分需要总分

6\cdot80=480

，因此第六次至少需要

480-385=95

。

所以正确答案是 E。

The five scores sum to

90+80+70+60+85=385,

giving an average of

77.

The goal is a new average of at least

80.

Six tests averaging

80

must total

6\cdot80=480,

so the sixth score must be at least

480-385=95.

Thus, the correct answer is E.

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