Question

Josanna 到目前为止的考试分数为 $90$ 、 $80$ 、 $70$ 、 $60$ 和 $85$ 。她的目标是在下一次考试后把考试平均分至少提高 $3$ 分。她至少需要在下一次考试中得到多少分？

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?

$80$

$82$

$85$

$90$

$95$

答案：E

知识点：平均数逆推法

难度评级：870

小提示：

求当前总分和目标平均分。

Find the current total score and target average

大提示：

第六次考试后总分必须达到 $6\cdot80$ 。

The sixth score must bring the total to $6\cdot80$

解答：

她当前的平均分为 $\dfrac{90+80+70+60+85}5 = 77\text{，}$ 而总分为 $385$ 。目标平均分为 $80$ ，所以六次考试所需的总分为 $80\cdot 6$ 。因此下一次考试至少需要得 $80\cdot 6-385 = 95\text{。}$

所以正确答案是 E。

Her current average is $\dfrac{90+80+70+60+85}5 = 77,$ and the sum of her scores is $385.$ The desired average is then $80,$ so the sum of scores required is $80\cdot 6.$ Therefore, the answer is $80\cdot 6-385 = 95.$

Thus, the correct answer is E .

2011 AMC 10B 第 2 题

答案：E

难度评级：870

小提示：

大提示：

解答：

其他年份的第 2 题