qingjiao several contraversial math jj

andrewcan

1. 10个字母选若干个组成a sequence，问选5个字母和选4个字母的数目的比率? =6/1 （4次）
【机委】6:1

2.DS题,说农场里有animals 60头，其中2/3either猪or牛,问猪(或者牛)的数目是多少?
(1) the number of cow is more than twice as many as the number of pigs.
（2）pigs的数more than 12
[确认]C
我选E
3 .problem solving有一道新题看不太懂，我背了下来，请大家补充，谢谢！
the prosibility of A increased is 54%, the prosibility of b increased is 68%, what's the "greatest prosibility of neither of the 2 event occur"?
a) 22%， b) 32% ， c) 37%， d)46%， e)??
[思路]这是求两个事件都不发生的概率吧。
我选32，完全重合，取最大的补集，
最小的话，应该是22，大家呢？

Many thanks!



[em27]

pear

1. P(10,5)/P(10,4)=6

pear

[讨论]
2.由条件(1)有:
   Pig+Cow=60*2/3
   Cow=3Pig
=> P=10,C=30
所以我的答案是 A, 为什么是C?

andrewcan

to Pear:
About 2. now I realize it:

From 1):  C : P  can be  30 - 10;  29 - 11;  28 - 12........
2) alone is not sufficent.
combine:   only one possibility: C : P = 27 : 13.     for 26:14,  26 is less than 2 X 14.

do you agree with me?

猫猫头

2、是C，可以是两种情况：27，13；28，12

猫猫头

1、correct
3、32%，确定

lisaislisa

2.one possibility 27+13 , 28+12 is against ' more than 12'
3.not A=46%  not B=32% =>neither occur = 32%

^^