Question

Ryan 在一份有 $25$ 道题的测试中答对了 $80\%$ ，在一份有 $40$ 道题的测试中答对了 $90\%$ ，在一份有 $10$ 道题的测试中答对了 $70\%$ 。所有题目中 Ryan 答对了百分之多少？

Ryan got $80\%$ of the problems correct on a $25$ -problem test, $90\%$ on a $40$ -problem test, and $70\%$ on a $10$ -problem test. What percent of all the problems did Ryan answer correctly?

$\ 63$

$\ 75$

$\ 80$

$\ 84$

$\ 86$

答案：D

知识点：百分数

难度评级：960

解答：

三份测试共有 $25+40+10 = 75$ 题。

第一份测试答对 $0.8\cdot25 = 20$ 题。

第二份测试答对 $0.9\cdot40 = 36$ 题。

第三份测试答对 $0.7\cdot10 = 7$ 题。

因此他总共答对 $20+36+7=63$ 题，答对比例为 $\dfrac{63}{75} = 84\%$ 。

所以正确答案是 D。

There were a total of $25+40+10 = 75$ problems.

On the first test, he solved $0.8\cdot25 = 20$ problems.

On the second test, he solved $0.9\cdot40 = 36$ problems.

On the third test, he solved $0.7\cdot10 = 7$ problems.

Therefore, he solved a total of $20+36+7=63.$ This means the fraction he solved is $\dfrac{63}{75} = 84\%.$

Therefore, the answer is D .

2010 AMC 8 第 9 题

答案：D

难度评级：960

解答：

其他年份的第 9 题