有些题目还是没弄明白

syf1985085

Q2:

A certain characteristic in a large population has a distribution that is symmetric about the mean m.  If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m +
                d ?

 

A.     16%

B.     32%

C.     48%

D.     84%

E.      92%

 

If the units digit of the three-digit positive integer k is nonzero, what is the tens digit of k?

(1)     The tens digit of k + 9 is 3.

(2)     The tens digit of k + 4 is 2.

                  

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Q13:

Of the books standing in a row on a shelf, an atlas is the 30th book from the left and the 33rd book from the right.  If 2 books to the left of the atlas and 4 books to the right of the atlas are removed from the shelf, how many books will be left on the shelf?

 

A.     56

B.     57

C.     58

D.     61

E.      63

Q20:

If the sum of three integers is even, is the product of the three integers a multiple of 4 ?

(1)     All three integers are equal.

(2)     All three integers are even.

(答案是Ｄ，但是如果条件一也对，例如：６＋６＋６？？不是就不能满足题目了？

The toll for crossing a certain bridge is $0.75 each crossing.  Drivers who frequently use the bridge may instead purchase a sticker each month for $13.00 and then pay only $0.30 each crossing during that month.  If a particular driver will cross the bridge twice on each of x days next month and will not cross the bridge on any other day, what is the least value of x for which this driver can save money by using the sticker?

 

A.     14

B.     15

C.     16

D.     28

E.      29

smjaney

If the sum of three integers is even, is the product of the three integers a multiple of 4 ?

(1)     All three integers are equal.

(2)     All three integers are even.

是三个数乘积为4的倍数哦，乘积的话就好理解了吧？

因为三个数的和是偶数，则要么一偶两奇，要么三偶。当三个数相等时，必定三偶。

只要有两个偶数相乘，乘积就必定是4的倍数了，何况三个。。。

所以选D。

不过这个题目需要默认一条：0是任何数的倍数。。。

如果是实战，我估计题目会说是nonzero integers的。

[此贴子已经被作者于2008-3-25 15:54:16编辑过]

smjaney

If the units digit of the three-digit positive integer k is nonzero, what is the tens digit of k?

(1)     The tens digit of k + 9 is 3.

(2)     The tens digit of k + 4 is 2.

应该是A

设 K = XYZ，1<Z<9（打不出小于等于号，将就着看吧。。。）

（1）K+9的十位实际只看Z+9就行了，由已知必有10<Z+9<18，十位进1推出Y=3，所以没进位之前，K的十位Y=2，SUFFICIENT

（2）当1<Z<9时，5<Z+4<13，有可能进位，有可能不进，由已知无法确定，UNSUFFICIENT

[此贴子已经被作者于2008-3-25 15:16:00编辑过]

smjaney

Of the books standing in a row on a shelf, an atlas is the 30th book from the left and the 33rd book from the right.  If 2 books to the left of the atlas and 4 books to the right of the atlas are removed from the shelf, how many books will be left on the shelf?

这道选A。

左手边数第30本 = 右手边数第33本。

书的总数=30+33-1=62本。

拿掉2+4=6本，62-6=56，还剩56本。

题目第二句除了2和4和remove之外，关于位置的描述都是无关信息。

[此贴子已经被作者于2008-3-25 15:55:36编辑过]

smjaney

The toll for crossing a certain bridge is $0.75 each crossing.  Drivers who frequently use the bridge may instead purchase a sticker each month for $13.00 and then pay only $0.30 each crossing during that month.  If a particular driver will cross the bridge twice on each of x days next month and will not cross the bridge on any other day, what is the least value of x for which this driver can save money by using the sticker?

选B

由已知列等式：

0.75*2X-(13+0.3*2X) = 0.9X-13

若要省钱，必须0.9X-13>0

推出X>14.4

满足结论的最小值是B选项，X=15。

smjaney

A certain characteristic in a large population has a distribution that is symmetric about the mean m.  If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m + d ?

这道是选D么？

由已知，数列是对称均匀分布在平均数M两边的，68%是WITHIN一个方差D的话，即取值在M-D和M+D之间，即这68%的数小于M+D。

而另外32%的数WITHOUT方差D，也就是说更加离散，又因为均匀对称，所以大于M+D的和小于M-D的各占一半，即16%的数小于M+D。

68+16=84。

[此贴子已经被作者于2008-3-25 15:53:18编辑过]