2017年9月3日GRE考试数学机经预测

题目

1. Which of the following operations carried out on both the numerator and the denominator of a fraction will always produce an equivalent fraction? Indicate all such operations?

A. Adding 2

B. Multiplying by 5

C. Dividing by 100

答案：B C

解析：题目问以下哪些在分子和分母上同时进行的做法不会让分数发生变化?A各加2错误。B都乘5，上下抵消还是原值，正确。C都除以100，同样上下抵消，正确。所以选BC。

2. In a certain medical group, Dr. Schwartz schedules appointments to begin 30 minutes apart, Dr. Ramirez schedules appointments to begin 25 minutes apart, and Dr. Wu schedules appointments to begin 50 minutes apart. All three doctors schedule their first appointments to begin at 8:00 in the morning, which are followed by their successive appointments throughout the day without breaks. Other than at 8:00 in the morning, at what times before 1:30 in the afternoon do all three doctors schedule their appointments to begin at the same time? Indicate all such times

A. 9:30 in the morning

B. 10:30 in the morning

C. 11:30 in the morning

D. 12:00 noon

E. 1:00 in the afternoon

答案：B E

解析：S是每30min有一次预约， R每25min，W每50min，中间没有停顿。题目问从早上8点到13:30之间，抛开早上8点那次，还有那几个时间点是这三个医生同时开始一个预约的。解答时先求出这三个时间的最小公倍数，也就是150分钟，说明每隔2.5个小时这三个医生会同时开始一项新的预约。则在给定的时间段内，10:30和13：00这两个时间他们会同时开始新的预约，所以选BE。

3. Set A has 50 members and set B has 53 members. At least 2 of the members in set A are not in set B. Which of the following could be the number of members in set B that are not in set A ? Indicate all such numbers.

A. 53

B. 5

C. 13

D. 25

E. 50

答案：A B C D E

解析：题目说至少有两个在A里面的数不在B里，那么完全有可能所有在A里的数都不在B中，所以B中所有的数就可以都不在A里面了。两个极值可得出范围：

1. A中48个成员也同时在B中, 得出符合所得要求(in set B that are not in set A)的最小值53-48=5;

2. A中没有成员同时在B中, 得出符合所得要求(in set B that are not in set A)的最大值53-0=53

选项所有数据均在范围内，因此全选。

What is the area of triangle ABC shown above?

A. 18

B. 20

C. 12√3

D. 18√3

E. 36

答案：D

解析：30,60,90度内角三角形变长特殊比例为：1：√3：2，因此对应AB和AC长度分别为6和6√3，三角形面积为18√3，选D。

5. Quantity A：the sum of the first 7 positive integers

Quantity B：7 times the median of the first 7 positive integers

A. Quantity A is greater.

B. Quantity B is greater.

C. The two quantities are equal.

D. The relationship cannot be determined from the information given.

答案：C

解析：QUANT A前7个正整数，也就是1到7之和为28. QUANT B前7个正整数里中位数的7倍，也就是4的7倍为28. 两者相等，所以选C。