gwd-6-13 新疑惑，恳请指点

saroya

Q13:

Lyme disease is caused by a bacterium transmitted to humans by deer ticks.  Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white-footed mice.  However, certain other species on which the larval feed do not harbor the bacterium.  Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium―and hence the number of people contracting Lyme disease—would likely decline.

 

Which of the following, if true, most strengthens the argument?

 

1. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans.
           
2. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice.
           
3. A deer tick feeds only once while in the larval stage.
           
4. A single host animal can be the source of bacteria for many tick larval.
5. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans

答案C 但我觉得取非不削弱阿 面对增多的other species 和原有的mice 吃几次 比 吃一次 难道吃到other species的几率变大？ 这是典型的概率知识 概率是不变的        请大家指路！ 多谢了！

lawyer_1

如果如C所说在LARCAL STAGE只吃一次，则infected white-footed mice和certain other species 就有排斥关系，吃这就不吃那。所以certain other species 的POPULATION增加,意味着吃certain other species 的比例增加，吃infected white-footed mice的比例减少。所以感染病的人也减少。所以才加强。

skyyuki11

假设吃到other species的概率为1/a, 吃到white mice的概率为1-1/a，吃到white mice 就感染，吃得次数越多(n次），吃到white mice的概率越大，感染的概率就大1- （1/a）n次幂

parisping

以下是引用lawyer_1在2007-4-6 23:05:00的发言：
如果如C所说在LARCAL STAGE只吃一次，则infected white-footed mice和certain other species 就有排斥关系，吃这就不吃那。所以certain other species 的POPULATION增加,意味着吃certain other species 的比例增加，吃infected white-footed mice的比例减少。所以感染病的人也减少。所以才加强。

所以certain other species 的POPULATION增加,意味着吃certain other species 的比例增加

为什么呢？？吃得多不就population减少了？

won872

Premises: Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white-footed mice.  However, certain other species on which the larval feed do not harbor the bacterium

 

Conclusion: if the population of these other species were increased, the number of ticks acquiring the bacterium―and hence the number of people contracting Lyme disease—would likely decline.

 

C is correct: A deer tick feeds only once while in the larval stage.

 

The food content for deer lava can be divided into two Group:

1)      Infected mice, assuming to be X% of total food sources.

2)      Other spices, assuming to be Y% of total food sources.

 

The probability of deer lava never contacted and infected with bacterium is:

P()= 1-( Y%)^n or 1-(1- X%)^n  

where “n” denotes number of trails that lava feeds

both X% and 1-Y% are less than 1, and they are fractions.

 

Hence the greater number of n the higher the probability that lava will infected with such desease. Remember only once fed on the infected mice is enough to cause the infection for lava; both Y% and 1-X% are less than 1, and they are fractions.

[此贴子已经被作者于2008-12-9 1:37:54编辑过]

delan714

如果如C所说在LARCAL STAGE只吃一次，则infected white-footed mice和certain other species 就有排斥关系，吃这就不吃那。所以certain other species 的POPULATION增加,意味着吃certain other species 的比例增加，吃infected white-footed mice的比例减少。所以感染病的人也减少。所以才加强。

我想请问，如果在LARCAL STAGE不只吃一次，就算吃了两三次，infected white-footed mice和certain other species 就不存在排斥关系了吗。certain “other” species ，应该是除了infected white-footed mice之外的和它不会重合的集合

jbc88

如果如C所说在LARCAL STAGE只吃一次，则infected white-footed mice和certain other species 就有排斥关系，吃这就不吃那。所以certain other species 的POPULATION增加,意味着吃certain other species 的比例增加，吃infected white-footed mice的比例减少。所以感染病的人也减少。所以才加强。

-- by 会员 lawyer_1 (2007/4/6 23:05:00)

说得多好啊！
真牛~