GMAT数学题求详解A 准备了4个不同的信封和对应的4封信,现在他随机的把4封信放入4个信封（每个信封都有一封信）.问恰巧只有一封信正确地放入对应信封的概率有多大?我发现每到难一点的概率题我就容易蒙圈啊!有没有高人有什么好方法的!

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• GMAT数学题求详解A 准备了4个不同的信封和对应的4封信,现在他随机的把4封信放入4个信封（每个信封都有一封信）.问恰巧只有一封信正确地放入对应信封的概率有多大?我发现每到难一点的概率题我就容易蒙圈啊!有没有高人有什么好方法的!
• gmat数学题 Last month 15 homes were sold in Town X.The average (arithmetic mean) sale price of the homes was $150,000 and the median sale price was $130,000.Which of the following statements must be true?I.At least one of the homes was sold for more than $165,000.II.At least one of the homes was sold for more than $130,000 and less than $150,000.III.At least one of the homes was sold for less than $130,000.A.I onlyB.II onlyC.III onlyD.I and IIE.I and III
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