21. 数学题整理----理工科的就不要看了.docx

修改后的资料名：GRE数学题整理，看看你会吗 资料类型：练习题 资料简介： George earned 80,85,and 90 on the first 3 tests in his geography class. Because he didnt have time to study, he decides to guess randomly on the final test. That test has 10 true-false questions, each worth 10 points. What is the probability his final average is more than 85? 第一个的话，它说平均分要多于85，那么这一门课多于85分才满足，所以对9题或者10题才行，对一个概率是1/2，全对为1/1024，对9题的话意味着只错1题，错一题有10种可能性，所以概率为10×1/1024，那么加起来11/1024 The company at which mark is employed has 80 employees, each of whom has a different salary. Marks salary of 43,700 is the second highest salary in the first quartile of 80 salaries. If the company were to hire 8 new employees at salaries that are less than the lowest of the 80 salaries, what would Marks salary be with respect to the quartiles of the 88 salaries at the company, assuming no other changes in the salaries? Key: the 5th-lowest salary in the second quartile. 第二个关键是看懂意思，如果编个号的话，1～80号，1号薪水最低，他是第一个1/4（即前20人中）中第二多的，那么他应该在19号位置。新来了8个人，薪水都比1号低，所以都在1号前面，此时他变成了27号。在88个人中，每1/4有22个人，27号位于第二个1/4中从低往高数的第5位。 A school group charters 3 identical buses and occupies 4/5 of the seats. After 1/4 of the passengers leave, the remaining passengers use only 2 of the buses. QA: The fraction of the seats on the 2 buses that are now occupied; QB: 9/10 设每辆车有a个座位，则一共有3a个座位，总人数为4/5乘以3a=12/5a。走了1/4乘以12/5a=3/5a人，还剩下9/5a人，这些人有2a个座位可坐。则比例为9/5a÷2a=9/10. In a single tennis tournament that has 125 entrants, a player is eliminated whenever he loses a match. How many matches are played in the entire tournament? 头一轮应该有62场比赛，124个人参加，剩下一个人轮空 进入第二轮有62个优胜者加上幸者共计63个人..第二轮有31场比赛共计62个人参加,外加一个轮空 进入第三轮有31个优胜者外加一个幸者参加，共计32个..所以有16场比赛 进入第四轮的有16个人,第四轮有8场比赛 第五轮有4场. 第六轮有2场.第七轮有一场 最后加起来总共有62+31+16+8+4+2+1=124。 A jar contains n red and n green marbles where n=2. You pick 2 marbles from the jar. QA: Number of ways to pick one of each color; QB: n平方 A number is a palindrome if it reads exactly the same from right to left as it does from left to right. For example, 959 and 2