sgmater

No.14
if the question is 求前40项的百位数的和是几？ the answer is 38
But since the questions is 求前40项和的百位数是几？
The answer should be 2, right?

sgmater

Hi oddyuibe,

Since nobody answers my questions under Math Questions Thred. I just try to post them here for good luck! I will take the test on 6/7!

1. [3-31]3. A和B读书10周，问哪个平均每周读的书多？
（1）twice the average books read by A per week is greater than 5 less than twice the average books read by B per week
（2）A和B中一人3周读了（具体数）本书
[确认] A

Why A? From A we can get either (A: 2 B:4  then  2*2>4*2-5) or (A:5 B:4 then 5*2>4*2-5)

2. [3-31]43.一个RANGE的题，集合T中的每个数都在集合S中，问集合T的Range《集合S的Range吗
1） 集合T中有6个数
2） 集合S中有7个数
[确认]:     C

Why C? range T should always < or = Range S. For example the T is {1,2,3,5,6,7} and S is {1,2,3,4,5,6,7} the range equal. But if T is {1,2,3,4,5,6} the the range different.

3. [3-31] 91. 7个XX重量不同，合计重量是78.3KG，问MEDIAN？
1)4个最轻的XX重量合计28KG
2)4个最重的XX平均重量是14KG
[确认]: C

Can any one give me some hint here?

4. [4-24]12) 7位数的电话号码。前三位数相同时是一个exchange，问282000个电话号码有多少个exchangs?答曰：29（这道题算是难的了）

What does this questions mean?

5. [4-25] 17) 一环型上有5个槽位，a必在一个槽位，b在a旁边，其它3个槽任放，问几种方法。
我选2p2，2
[确认]：60
[思路]：先选一个位置放a, 为C(5,1); 再从a边上的两个槽里选一个放b,为C(2,1); 其余的三个任意放，为P(3,3)
所以答案为：C(5,1)*C(2,1)*P(3,3)=5*2*6=60

If a必在一个槽位, why we need C(5,1)? it should just be C(2,1)*P(3,3) , right?

6.[5-1]13. 一社区有45户, 订报纸, 有 R, S, T 三种报,给出了三种报的订户人数分别是, S1=28, S2=17, S3=12,then, subscribe, both R&S, b1=9, both S&T b2=8, both R&T b3=7; Now 给出了一个重要条件, 订了三种的和什么都没有订的人,一样. 然后说, at least subscribe one kind of newspaper,29.
问: Subscribe only one kind Newspaper 的人数 X=?
[讨论]：X=S1+S2+S3-2B1-2B2-2B3+3a, 其中a是三种报纸都订了的户数 a=45-29=16

I don't understand above. Why just use 29-b1-b2-b3+a= 21 ?

7.[5-1] 47．用C.I.R.L.E 五个字母组成六个字母的词，C和C之间必须隔开，多少种？
[确认]：5P(6,6)-P(5,5)
[思路]：先不考虑C和C相邻的情况，按照六个位置进行全排列为5P(6,6)
再减去两个C相邻的情况，在这种情况下，把两个C看成一个元素，有P(5,5)中情况，所以答案是5P(6,6)-P(5,5)

Totally confused. How five letter to constitute a six letter word? Maybe the questions is use CIRCLE rather than CIRLE. So the answer should be
P(6,6)/P(2,2) - P (5,5), right?

8. [5-1] 48．ds 以速度p1完成路程s1所需时间比以速度p2完成路程s2所需时间长？
(1)p1比p2大30
(2)s1比s2大30
[确认]：C
[思路]：以速度p1完成路程s1所需时间:S1/P1=(S2+30)/(P2+30); 以速度p2完成路程s2所需时间:S2/P2
真分数分子分母同加上相等的数，分数的值越来越大。假分数相反。所以，可以判断。

How do we know S2/P2 is 真分数 or 假分数 to 判断? Are we assuming the real questions will give real number for S2 and P2? If not then answer should be E, right?