行程问题：

 

At the end of each day, the amount of water in a magic cup is twice what it was at the beginning of the day. If the cup is full at the end of 2017th day, then it was 1/4 full at the end of the ? day

A) 504th   B) 505th     C) 2015th    D) 2016th

 

参考答案：A

解析：本题与昨天第三题相似，但需要注意每一天晚上杯子里的水是早上的两倍，如果第2017天晚上杯子满了，求第多少天杯子里的水是四分之一？本题有两种做法，第一种反推。第2017天晚上满了，那么第2016天晚上应该是二分之一，第2015天是四分之一；第二种列方程，设第n天是四分之一，那么x乘以2²⁰¹⁷等于1。X乘以2ⁿ等于1/4，求解n=2015

 

My final score in a competition is the average of my scores on 5 rounds. To get a final score of 88 after getting 84, 80 and 92 on the first 3 rounds, what must be my average score for the last 2 rounds?

A) 88    B) 99    C)92    D)96

参考答案：C

解析：比赛共5轮，最终成绩为5轮成绩的平均分。前三轮比赛成绩分别为84,80,92，如果最终成绩为88，求最后两轮的平均成绩。列方程求解。设最后两轮平均成绩为x，2x+84+80+92=88×5，x=92

 

Ted, Rick and Sam painted a wall together. Ted painted 80% more of the wall than Sam painted. Sam painted 40% less than Rick. Ted painted ___ of the amount that Rick painted.

A) 102%     B)108%      C) 120%    D)140%

参考答案：B

解析：三个人一起刷墙。Ted比Sam多刷80%，Sam比Rick少刷40%，求Ted刷的墙是Rick的多少？设Rick刷了x，则Sam刷了0.6x，Ted刷了1.8乘以0.6x等于1.08x，1.08x除以x等于1.08。

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