AMC8 2010

AMC8 2010 · Q9

AMC8 2010 · Q9. It mainly tests Percent, Averages (mean).

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?

瑞安在一份25题的测试中答对了80%，在一份40题的测试中答对了90%，在一份10题的测试中答对了70%。瑞安全部题目答对的百分比是多少？

(A) 63 63

(B) 75 75

(D) 84 84

(E) 86 86

Answer

Correct choice: (D)

正确答案：（D）

Solution

Ryan answered $(0.8)(25)=20$ problems correct on the first test, $(0.9)(40)=36$ on the second, and $(0.7)(10)=7$ on the third. This amounts to a total of $20+36+7=63$ problems correct. The total number of problems is $25+40+10=75.$ Therefore, the percentage is $\dfrac{63}{75} = 84\% \rightarrow \boxed{\textbf{(D)}\ 84}$

瑞安第一份测试答对 $(0.8)(25)=20$ 题，第二份 $(0.9)(40)=36$ 题，第三份 $(0.7)(10)=7$ 题。总共答对 $20+36+7=63$ 题。总题数 $25+40+10=75$。因此，百分比是 $\dfrac{63}{75} = 84\% \rightarrow \boxed{\textbf{(D)}\ 84}$

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