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[资料分享] 【SAT每日一题】2012年7月20 Mathematics > Standard Multiple Choice [复制链接]

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发表于 2012-7-23 22:25:13 |显示全部楼层
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. & R. m& Z- j7 t: Q& M$ G; Y
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In 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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解析:6 g) d0 c, ]# h, m

8 F& p$ K9 b8 c/ Q; g8 X$ ~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.
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