SAT考试数学练习题SAT Math Practice 4
☆6. If f(x) = (x + 2) / (x-2) for all integers except x=2, which of the following has the greatest value?
A. f(-1)
B. f(0)
C. f(1)
D. f(3)
E. f(4)
☆7. ABCD is a square of side 3, and E and F are the mid points of sides AB and BC respectively. What is the area of the quadrilateral EBFD ?
A. 2.25
B. 3
C. 4
D. 4.5
E. 6
☆8. If n ≠ 0, which of the following must be greater than n?
I 2n
II n2
III 2 - n
A. I only
B. II only
C. I and II only
D. II and III only
E. None
☆9. After being dropped a certain ball always bounces back to 2/5 of the height of its previous bounce. After the first bounce it reaches a height of 125 inches. How high (in inches) will it reach after its fourth bounce?
A. 20
B. 15
C. 8
D. 5
E. 3.2
☆10. n and p are integers greater than 1
5n is the square of a number
75np is the cube of a number.
The smallest value for n + p is
A. 14
B. 18
C. 20
D. 30
E. 50
SAT考试数学练习题SAT Math Practice 4参考答案
☆6.Correct Answer: D
Explanation:
You can solve this by back solving – substitute the answer choices in the expression and see which gives the greatest value.sat
A (-1 + 2) / (-1-2) = -2 / 2 = -1;
B (0 + 2) / (0-2) = 2/ -2 = -1;
C (1 + 2) / (1-2) = 3/-1 = -3;
D (3 + 2) / (3-2) = 5/1 = 5;
E (4+ 2) / (4-2) = 6/2 = 3
If you had just chosen the largest value for x you would have been wrong. So although it looks a long method, it is actually quick and accurate since the numbers are really simple and you can do the math in your head.
☆7.Correct Answer: D
Explanation:
(Total area of square - sum of the areas of triangles ADE and DCF) will give the area of the quadrilateral
9 - (2 x ? x 3 x 1.5) = 4.5
☆8.Correct Answer: E
Explanation:
Remember that n could be positive negative or a fraction. Try out a few cases:
In case I, if n is -1, then 2n is less than n.
In case II, if n is a fraction such as ? then n2 will be less than n.
In case III, if n is 2, then 2-n = 0, which is less than n.
Therefore, none of the choices must be greater than n
☆9.Correct Answer: C
Explanation:
If after each bounce it reaches 2/5 of the previous height, then after the second bounce it will reach 2/5 x 125. After the third it will reach 2/5 x 2/5 x 125. After the fourth it will reach 2/5 x 2/5 x 2/5 x 125. This cancels down to 2 x 2 x 2 = 8
☆10.Correct Answer: A
Explanation:
The smallest value for n such that 5n is a square is 5.
75np can now be written as 75 x 5 x p.
This gives prime factors.... 3 x 5 x 5 x 5 x p
To make the expression a perfect cube, p will have to have factors 3 x 3 , and hence p =9
n + p = 5 + 9 = 14