2020年1月22日GRE数学机经预测

What are the x-intercepts of the parabola defined by theequation y =2x2–8x –90?

Indicate allx-intercepts.

A. -10

B. -9

C. -5

D. -4

E. 4

F. 5

G. 9

H. 10

解析：C, G

因为求x轴截距，所以y=0，所以2x2–8x –90=0，所以(2x+10)(x-9)=0. 所以x= -5, 或者x=9. 所以选C,G.

The system of equations has how many solutions?

3x - 6y = 9

2y - x - 3 = 0

A. None

B. Exactly 1

C. Exactly 2

D. Exactly 3

E. Infinitely many

解析：B

因为3x - 6y = 9，所以x-2y=3. 因为2y - x - 3 = 0，所以

2y-x=3. 所以x-2y=2y-x. 所以x=0,y=0.只有这个种可能。所以选B.

If x=3k/√5 and k>0， which of the following must be true?

解析：C

因为，所以x=(3√5)/5 k，所以k

For the 3 numbers in a certain list, the average (arithmetic mean) and the median are equal to 16. If the greatest number in the List is 14 greater than the least number, what is the greatest number in the list?

解析：23

设最小的数为x,因为的数比最小的数大14，所以的数为x+14.因为这三个数的平均值为16，且中间的数值为16，所以

(x+16+(x+14))/3=16.所以x=9. 所以的数为9+14=23.

When thepositive integer dis divided by 12, the remainder is 5. Whatis the remainder when d is divided by 8 ?

A. 1

B.3

C.5

D.6

E.7

解析：A

正整数d被12整除后余5，所以正整数d为12*5+5=65. 所以〖65〗^2除以8等于528余1.所以选A。

In agroup of 60 people, the average (arithmetic mean) age of the 40 females is 60,and the average age of the 20 males

is 70.

Column A ColumnB

Average age of all 60 people 65

A. Thequantity in Column A is greater

B. Thequantity in Column B is greater

C. The twoquantities are equal

D. Therelationship cannot be determined from the information given

解析：

因为一共有60个人，40个人的平均年龄是60岁，20个人的平均年龄是70岁。所以这60个人的平均年龄为(40*60+20*70)/60=63.33.

63.33<65,所以B更大。所以选B。