【SAT每日一题】2012年7月20 Mathematics > Standard Multiple Choice

滚吧肥汤圆UID: 3272378

考试类型: Mathematics > Standard Multiple Choice
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Read the following SAT test question and then click on a button to select your answer.

9 E5 Q; ?0 e8 _" v6 Y3 Y' oIn an solution of water and alcohol, the ratio by mass of water to alcohol is 3 to1 . If 12 grams of a solution consisting of 2 grams water for each gram of alcohol is added to the  solution, what fraction by mass of the new solution is alcohol?
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E. [img] http://sat.collegeboard.org/math ... 012/20120720_11.png[/img]
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正确答案:B

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To find what fraction by mass of the new solution is alcohol, you can find how many grams of alcohol are in the final solution of 20 grams. Since the solution is 1 part alcohol to 3 parts water, it is alcohol. So it 2contains  grams of alcohol. Similarly, the solution is alcohol by mass, so it contains 4 grams of alcohol. Thus, the final solution contains 6 grams of alcohol, so , or , of it is alcohol.