2月25号换题库-GMAT数学新题答案整理贴（240-300）

Aseiman

240.
k为正整数，7的K次方的十位数字为0，则下列哪些could be true

a)7的k次方的个位数字为1

b)7的K次方的个位数字为5

c)k is a multiple of 4

选a)
c)

7的个位数 以
7， 9， 3， 1 循环， à a could be true

         同理
b à could not true

k is a multiple of 4
à could be

241.
x为负偶数，y为负数，则y的x次方范围

选0到1

y^x = 1 / (y^(-x)), y^(-x) > 0
y @ (-1, 0)
y^x > 1
y@(-$, -1)
0< y^x < 1

242.
2^x>6,x范围
a)x>2
b)x>3
c)x<5
选a)

应该有 x 是整数的条件吧， 要不  不会是A

243.
DS:能否求出一月与二月产量之比？

     一.两个月产量之和为a（已知数）

     二.一月产量占两个月产量之和的百分之多少（已知数）      选B

         条件一：

a + b = t
a/b = s à
bs + b = t à s = ( t – b ) / b, b unknown à 条件一不满足

         条件二：

a /(a+b) = x à (a + b) / a = 1/x à 1 + b/a = 1/x à b/a = 1/x – 1 à B

jaffa23

many  thanks @@

allygmat7

many  thanks !@

Aseiman

267.         3x-4y>0, is x>y? 1) x= 1     2) y=2 : (數字不確定)
这题是不是出错了？
3x – 4y > 0  x > 4/3y > y, 条件没什么用啊

268.        (1/8)^2 (这题用分数算, 答案全是分数的形态）: Answer（0.25)^3
这不就是 1/8 * 1/8 = 1/64    淡定。。。。

269.          Given a rectangle, with sides PQRS. The area is 4根号3, PR is twice of PQ (PR是对角,斜边). What is PR?
xy = 4（根号3）
2x = 根号（x^2 + y^2）  x = 2  PR = 4

另：x * (根号3) * x = 4根号3 x = 2  PR = 4  (一个角是30度)

270.         圆内切一个长方形，一条边长2，另一条边长12，求圆半径。算出来根号下37。
144 + 4 = 148  所以圆直径是 2 根号37 所以。。。

Aseiman

292.        If y = [4(n+1)-5]/[(n+1)(n+2)], which of the following has the greatest value?
   A.   -1/y
   B.    (1/y)2
   C.    y2
    D.   (1/2y)
E.    y
当 n = 0 时 y = 1/2  代入 得 B
293.         If a store sells three kinds of belts and each account for 20 percent, 50 percent, and 30percent of the revenues respectively, what is the average price for each belt sold?
     Price of each belt is $5, $3, and $10 respectively
不会做

294.         A museum has 40 exhibits, total of 2000 visits last month. What is the average revenue for each exhibit?
    1) Revenue from each child ticket and adult ticket sold are $8 and $12 respectively
2) More than half of the exhibit account for revenue of $2000
average revenue for each exhibit  revenue / 40  revenue ?
from 1)  x + y = 2000, 8x + 12y  无法求出  not A
from 2)  revenue 无法求出
union：  8x + 12y > 2000  无法求出 revenue so E
295.         A triangle is on the xy plane, with coordinates A, B, and C. B and C coordinates are given on the plane. What is the coordinate of A?  1) AB=x 2) BC=y (x and y are given as numbers, but I forgot them all!!) (Just try to image or learn the concept)
from 1) A点在以B为圆心x为半径的圆上 无法确定哪个点  not A
from 2) 只能求出BC的长度， 无法确定A点 not B
union:  不能确定A点 so E

296.         Is n a prime number? 1) n is a factor of 125     2) n is a factor of 75
遇到这种题 直接选E, 如果你能通过任何条件能判定一个数是不是素数， 你就能证明1 + 1 = 2 了

Aseiman

288.         If Integer x=5^m + 3^n, what is x?
     1)    mn = 20
     2)    m+n = 9
     x = ?  x = 5^m + 3^n  m, n
        from 1)  mn = 20 can not get m, n    so not  A
        from 2)  cannot get m, n             so not B
        union: C
289.         If n=(x-3)/(y-4),what is n?
     1) x=3
2) y=2
同上题  C


290.          Machine x can complete a task in 8 hours and machine y can complete the same task in 4hours. How much of a task does x completes if x and y are working together?
x 每小时完成任务的 1/8; y 每小时完成任务的 1/4
x, y一起做，每小时完成任务的 1/8 + 1/4即  3/8其中 x占1/8
x做1/3

291.         If n is an integer between 10 and 99 and n is divisible by 7, the remainder is 3, is n< 80?
    1) When n is divided by 5, the remainder is 0
2) When n is divisible by 3, the reminder is 0
Inclusive ?
n = 7m + 3
from 1)  n = 5k  n = 35t + 10, t = 0, 1, 2, 3, … so  not A
from 2)  n = 3s  n = 21a + 24  a = 0, 1, 2, 3, …so  not B
union  n = 35t + 10 , n = 3s  n = 105 k + 45 在 10 到 99 只有45满足条件 so C

Aseiman

284.        Is x > 5?
   1) x2> 25   这里应该是  x^2 吧？
   2)2x + 7 > 0   Answer: C
        from a)  x > 5 or x < -5   not A
        from b)  x > - 3.5   x > 5 or  -3.5 < x < 5  not B
        union  x > 5  C
       
285.         In a hospital, 40percent of the newborn are boys and 10 percent of them have weights greater than 3.18kg. And 10 percent of the newborn boys have weights greater than3.18kg. What percent of the newborn have weights greater than 3.18kg in the hospital?
   1) 20 percent of the newborn girls have weights less than 3.18kg
2) 6percent of the total new born have weights greater than 3.18kg

题目中的红色部分有用吗?  
60% of the newborn are girls  from 1)  80% of the newborn girls have weights no less than 3.18kg  we do not know what percent of newborn girls have weights equal to 3.18 kg.  can not get what percent of newborn girls have weights greater than 3.18kg  not A

from 2)   6% (什么意思？ total new born 与 newborn 不一样吗？)  B

286.         If  2.164 *1017– 5.12*1016 = 1.652 *10m , what is m?
这m是个负数，剩下的排除吧，就别算了，我是没有想到什么更好的办法，有人想到了， 告诉我一声，谢谢

287.         If |2x-5| = x-3, how many solutions does x have?
4x^2 – 20x + 25 = x^2 – 6x + 9  3x^2 – 14x + 16 =0 △ < 0  no solutions at all

Aseiman

280.        2到100间的偶数，其中能被1之外的奇数整除的数有几个？（题目几不清了）   六个（2， 4， 8， 16， 32， 64）
还是不会

281.        两位整数，知道个位是5，求十位是几， DS题
等补充吧

282.         One questionstates that hundredth digit is more than three times of the tenths digits of an integer, which of the following MUST be true. (这题是说一个 数, 百分之一的数大于三倍的十分之一数, 下列选项哪个是对的.
同意
283.        X is 20percent more than y which is 20 percent than z, w is 20 present less than x,how much greater than z is x. (答案选项是百分比的型式)   
x = 1.2y;  y = 1.2 z ;  w = 0.8x  x = 1.44z  so 44%
给w是做什么的？

Aseiman

276.        有一个三位数，知道个位是百位的2倍，这个数可以被3整除， 问可以得到那个是对的
      a十位是非零的数
      b十位是奇数
      c十位是三的倍数
        设 百，十，个位数分别是 a, b ,c
        c = 2a, a + b + c = 3n   3a + b = 3n
a)         当 b = 3 时  3(a + 1) = 3n  a) 不是必须的
b)        当 b = 6 时  3(a + 2) = 3n  b) 不是必须的
c)        假设 b 不是三的倍数 设 b / 3 模 1， 即 b = 3m + 1  3a + 3m + 1
 永不为可被3整除 　c) 是必须的
277.        说3a=2b, 2b=9c,问b/a+ c/b+c/a=?
3a = 9c c/a = 1/3  b/a = 3/2  c/b = 2/9    所求 = 37 / 18

278.         n可以被5整除？1）7的n次方-1， 2）7的N次方-3
在说什么呢？

279.        两线段有图，图上标黑的部分是小于（-0。5）和大于（1。5）的两线段，问下列不等式哪个能对应。选项大概都是绝对值X》=一个式子。我先化简最后一个选项，正确。就没有验算其它选项。（还是应该一一验算的，万一有什么没有发现的陷阱呢。但是如果时间紧张，这种题正确的策略还是从最后一个选项开始化简。
等补充。。。

Aseiman

271.        ︱x︱+x/2<4, x=?  (1)x>-12  (2)x<-6
1)  0 < x < 8/3  or -8< x <= 0   not A
2)  -8< x < -6  not B
union:  -8 < x < -6  E

272.         (a-x)(b-x)-4h^2=0是否有两个解? (1)a≠b (2)h≠0
设 b = a + n 由条件1)  n <> 0 ;   
(x-a)(x-b) = (2h)^2  (x-a)(x –a -n) –(2h)^2 = 0  (x-a)^2 – n(x-a) – (2h)^2 = 0;
        △= n^2 + 4 (2h)^2 > 0  有两解
from 2)  △ > 0
so D

273.        xy^2=z^3  问z^3>0?
     a.  x^2y>0
     b.  xy<0 ？ 记不清了
        we should determine whether xy^2 > 0 .
        form a)  x^2y > 0  y > 0 but we cannot know whether x is great or less than 0  no A
from b) xy < 0  即x,y 异号    when x > 0 : xy^2 > 0,  when x < 0 xy^2 < 0  not B
union:  y > 0, x,y异号  x < 0  xy^2 < 0  z^3 < 0  C

274.         1/6 (48)^22=?
8 * 48 ^21  (不会是求出具体的数吧？ 那样也太霸气外露了)

275.        求三角形面积，给了公式S=根号下：s(s-a(s-b)(s-c)其中s=1/2(a+b+c),给了abc
代入公式