[求助]PP3的4道题(2天就考了,拜托了!谢谢!)

salvador

以下是引用深谷幽兰在2006-4-23 14:35:00的发言：

.IF r and s are intergers and rs+s is odd, which of the following must be even?
a.r
b.s
c, r+s
d. rs-r
e. r^2+s
ANA: C
RS+S 是偶数, 则RS和S必须都是偶数=> S是偶数或R是偶数或都是ODD. => R+S不一定是偶数呀?

lz，题目说RS+S 是奇数，是敲错了还是看错了？

.

明白了. 看的时候把RS+S看成了EVEN.如果是奇数就好做了. 做题真是要仔细呀!

but if rs+s=s(r+1) is odd, s and r+1 should be odd, then r is even and s is odd, r+s is odd.

answer is D? open to discuss

深谷幽兰

以下是引用深谷幽兰在2006-4-23 14:35:00的发言：

.IF r and s are intergers and rs+s is odd, which of the following must be even?
a.r
b.s
c, r+s
d. rs-r
e. r^2+s
ANA: C
RS+S 是偶数, 则RS和S必须都是偶数=> S是偶数或R是偶数或都是ODD. => R+S不一定是偶数呀?

lz，题目说RS+S 是奇数，是敲错了还是看错了？

.

明白了. 看的时候把RS+S看成了EVEN.如果是奇数就好做了. 做题真是要仔细呀!

but if rs+s=s(r+1) is odd, s and r+1 should be odd, then r is even and s is odd, r+s is odd.

answer is D? open to discuss

SORRY,又看了一下. ANSWER IS "S". 但S可能为ODD,也可能为EVEN

salvador

晕倒了！

这样还是与题目不一致啊！不过这道题我也碰到过，不是很难，到时候仔细一点肯定能作对。

[此贴子已经被作者于2006-4-23 14:52:52编辑过]

scujean

.IF r and s are intergers and rs+s is odd, which of the following must be even?
a.r
b.s
c, r+s
d. rs-r
e. r^2+s
ANA: C
RS+S 是偶数, 则RS和S必须都是偶数=> S是偶数或R是偶数或都是ODD. => R+S不一定是偶数呀?

早上想破头就是想不出是C，原来是B

我的做法 rs+s is odd→s(r+1)=积

所以s=积，且(r+1)=积→r=积-1=偶

salvador

以下是引用scujean在2006-4-23 19:14:00的发言：

.IF r and s are intergers and rs+s is odd, which of the following must be even?
a.r
b.s
c, r+s
d. rs-r
e. r^2+s
ANA: C
RS+S 是偶数, 则RS和S必须都是偶数=> S是偶数或R是偶数或都是ODD. => R+S不一定是偶数呀?

早上想破头就是想不出是C，原来是B

我的做法 rs+s is odd→s(r+1)=积

所以s=积，且(r+1)=积→r=积-1=偶

your answer is a! but the correct answer is b? why?

[此贴子已经被作者于2006-4-23 20:11:59编辑过]

scujean

可能是题目哪里有问题..我的观念应该正确吧..

hitlzc

不好意思，深谷幽兰，我这两天很忙，才看到你的短信。

2.IF r and s are intergers and rs+s is odd, which of the following must be even?
a.r
b.s
c, r+s
d. rs-r
e. r^2+s
ANA: C
RS+S 是偶数, 则RS和S必须都是偶数=> S是偶数或R是偶数或都是ODD. => R+S不一定是偶数呀?

支持scujean的看法，选A

3. IF the operation is defined for all integers a and b by a@b=a+b-ab, which of the following statement must be true for all a, b,c,
ANS: (A@B)@C=A@(B@C)
不明白这是如何得来的?
代入去算了，

a@b=a+b-ab, (a@b)@c = (a+b-ab)@c = a@c+b@c-ab@c =a+c-ac+b+c-bc-ab-c+abc

=a+b+c-ac-bc-ab+abc

a@(b@c)= a@(b+c-bc)=a@b+a@c-a@bc =a+b-ab+a+c-ac-a-bc+abc

=a+b+c-ac-bc-ab+abc

另外就是这个算式a@b=a+b-ab和两个集合的并集的规律类似，AUB=A+B-AB

（AUB）UC=AU（BUC）

当然我认为前一种解法更保险一些，就是太慢。

4.a certain library accesses fines for overdue books as follows. on the first day that book is overdued, the total fine is $0.1, for each additional day that the book is overdue, the total fine is either increased by $0.30 or doubled,whichever results in the lesser amount. What is the total fine for a book on the fourth day it is overdue?
ANS: $0.7

http://forum.chasedream.com/dispbbs.asp?boardid=22&id=152966&star=1#1433693

[此贴子已经被作者于2006-4-24 14:57:26编辑过]

wsdoll

以下是引用hitlzc在2006-4-24 14:54:00的发言：

不好意思，深谷幽兰，我这两天很忙，才看到你的短信。

2.IF r and s are intergers and rs+s is odd, which of the following must be even?
a.r
b.s
c, r+s
d. rs-r
e. r^2+s
ANA: C
RS+S 是偶数, 则RS和S必须都是偶数=> S是偶数或R是偶数或都是ODD. => R+S不一定是偶数呀?

破解版题意是 rs+r 是 odd., 所以 r is odd, S is even. 选B.

lz 的条件选A 和 D.

phoenixfr

以下是引用wsdoll在2007-9-10 8:48:00的发言：

破解版题意是 rs+r 是 odd., 所以 r is odd, S is even. 选B.

lz 的条件选A 和 D.

我说怎么上面的答案感觉都不只一个……

5cheng

求助第一个的翻译和步骤！