41. Aisha's income in 2004 was 20 percent greater than her incomes in 2003. What is the ratio of Aisha's income in 2004 to her income in 2003?
A 1 to 5
B 5 to 6
C 6 to 5
D 5 to 1
E 20 to 1
Ans: C
解析： 设2003年Aisha's income为x，则2004的income为1.2x
income2004 : income2003=1.2x : x=6:5
解题要点：涉及比较，选择恰当的基准量，并用其表示其余未知量
42. What is the slope of line k in the x-y plane above?
A -5
B -1
C 0
D 1
E 5
Ans: D
解析： (x1,y1)=(5,0); (x2,y2)=(0,-5)
k=(y2-y1)/(x2-x1)=1
解题要点：坐标几何——斜率的求法。
43. b-3,b-1,b+2,b+3,b+4
The median of the five terms listed above is 5, where b is a constant. What is the average (arithmetic mean) of the five terms?
A 3
B 4
C 5
D 6
E 7
Ans: B
解析： b是常数，所以b-3>b-1>b+2>b+3>b+4?
b+2=5,b=3; ?
0,2,5,6,7
(0+2+5+6+7)/5=4
解题要点：掌握median和average(arithmetic mean)的概念及求法
44. During a one-year study, biologists observed the number of fish in a certain pond as well as the percent of the fish that were catfish. At the beginning of the year, there were 300 fish in the pond, of which 15 percent were catfish; and at the end of the year, there were 400 fish in the pond, of which 10 percent were catfish. From the beginning of the year to the end of the year, the number of catfish in the pond
A decreased by more than 5%
B decreased by 5%
C did not change
D increased by 5%
E increased by more than 5%
Ans: A
解析： catfish(beginning): 300*15%=45
catfish(end): 400*10%=40
decrease=(45-40)/45≈11%>5%
解题要点：文字题理解题意，找到含代数关系的关键语句
45. On a radio tower, a red light flashes every 6 seconds and a blue light flashes every 10 seconds. If both lights flash together at a certain time, how many seconds later will both lights flash together the next time?
Seconds
Ans: 30
解析：方法一
red light: 6,12,18,24,30,36,42,48,54,60,66,72,…
blue light: 10,20,30,40,50,60,70,80,90,10,…
方法二
求6,10的最小公倍数，为30
解题要点：时间点重叠问题——找最小公倍数
46. If a
Indicate all such numbers
A a-b
B a2-b2
C ab
D a2b
E a2b+ab2
Ans: BC
解析： A: a
B: a2-b2=(a+b)(a-b) a<0,b<0;a+b<0 由A得 a-b<0 (√)
C: a<0,b<0 ab>0 (√)
D: a2>0,b<0 a2b<0 (×)
E: a2b+ab2=ab(a+b) a<0,b<0;ab>0,a+b<0 (×)
47. If x>0, which of the following is equal to 1.25 percent of x?
A x/80
B x/8
C x/4
D 5x/8
E 3x/4
Ans: A
解析： 1.25%x=1.25x/100=x/80
解题要点：熟练掌握百分数、小数、分数间的转换
48. Alice earns d dollars and has t percent of what she earns deducted for taxes. How much of what she earns does Alice have left after taxes?
A d(1-100t) dollars
B d(1-10t) dollars
C d(1-t) dollars
D d(1-0.1 t) dollars
E d(1-0.01t) dollars
Ans: E
解析： d(1-t%)=d(1-0.01t)
解题要点： 文字题理解题意
t%=0.01t
49. A student made a conjecture that for any integer n, the integer 4n+3 is a prime number. Which of the following values of n could be used to disprove the student's conjecture?
Indicate all such values
A 1
B 3
C 4
D 6
E 7
Ans: BD
解析： A:n=1,4n+3=7 (×)
B:n=3,4n+3=15 (√)
C:n=4,4n+3=19 (×)
D:n=6,4n+3=27 (√)
E:n=7,4n+3=31 (×)
50. If x
A y+1
B y-1
C xy2
D xy
E xy
Ans: E
解析： A:y>x y+1>y>x (×)
B:y=-1 x=-3 y-1=-2>x (×)
C:y<-1 y2>1 xy2>x (×)
D:xy2 (×)