求问Prep上几道数学题, 请各路大虾帮忙，多谢！！

lingyixin101 · 发表于 2012-12-9 09:59:22

1. When 1000 children were inoculated with a certain vaccine, some developed inflammation at the site of the inoculation and some developed fever. How many of the children developed inflammation but not fever?
1) 880 children developed neither inflammation nor fever. 2) 20children developed fever.

2. Before being simplified, the instructions for computing income tax in country R were to add 2% of one's annual income to the averge(aritmetic mean) of 100 units of country R's currency and 1% of one's annual income , If the income is I , what is the income tax?
为什么答案是： 50 + I/400。。。

3. Did one of the 3 members of a certain team sell at least 2 raffle tickets yesterday?
1) THe 3 members sold a total of 6 raffle tickets yesterday. 2) No 2 of the members sold the same number of raffle tickets yesterday.

4. Durign an experiment, some water was removed from each of 6 water tanks. If the standard deviation of the volumes of water in the tasks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?
1) for each tank 30% was removed 2) The average volume at the end is 63 gallons.

Annapp · 发表于 2012-12-9 11:23:57

1. When 1000 children were inoculated with a certain vaccine, some developed inflammation at the site of the inoculation and some developed fever. How many of the children developed inflammation but not fever?
1) 880 children developed neither inflammation nor fever. 2) 20children developed fever.

2. Before being simplified, the instructions for computing income tax in country R were to add 2% of one's annual income to the averge(aritmetic mean) of 100 units of country R's currency and 1% of one's annual income , If the income is I , what is the income tax?
为什么答案是： 50 + I/400。。。

3. Did one of the 3 members of a certain team sell at least 2 raffle tickets yesterday?
1) THe 3 members sold a total of 6 raffle tickets yesterday. 2) No 2 of the members sold the same number of raffle tickets yesterday.

4. Durign an experiment, some water was removed from each of 6 water tanks. If the standard deviation of the volumes of water in the tasks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?
1) for each tank 30% was removed 2) The average volume at the end is 63 gallons.

-- by 会员 lingyixin101 (2012/12/9 9:59:22)

我做的不知道有没有错，你看一下吧~

1.C 用韦恩图做。
[attachimg]111174[/attachimg]
用方框代表全部1000人数，A代表 developed inflammation 的人数，B代表 developed fever的人数
要求的是：A-紫色斜线部分
1）黄色部分是880 → A+B-紫色斜线部分=1000-880=120 → 不知道B NS
2）B=20 NS
两个条件一起，S

2.这道题是题目理解的问题，很容易出错呃。。。我也错过。题目是这样的：
Before being simplified, the instructions for computing income tax in country R were to add 2% of one's annual income to the averge(aritmetic mean) of 100 units of country R's currency and 1% of one's annual income , If the income is I , what is the income tax?
就是说：R 国的所得税是这样计算的：年薪收入的 2%，再加上年薪收入 1% 与 100 元的平均.
步骤是I*2%+(100+1%*I)/2=50+I/40

3.D
条件1：三个人一共卖了6个，平均数是2个/人，因此无论如何都至少会有一个人卖了2个及以上 S
条件2：没有两个人卖出同样的个数。【注意】买东西隐含的条件就是销售个数为≥0的整数 ∴三个人销售量的最小可能是0,1,2，这样也是确定有一个人卖了2个 S

4.A
方差的性质：数组每个数同时乘/除同一个倍数，变化后的方差=原方差×倍数^2
数组每个数同时加/减同一个数。方差不变。
题目告诉了你初始方差，求变化后的方差
条件1：告诉了你同乘0.7 S
条件2：告诉你变化后的平均数，但是你不知道初始平均数，没办法判断方差怎么变 NS

lingyixin101 · 发表于 2012-12-9 18:59:33

给力，灰常谢谢！！

求问Prep上几道数学题, 请各路大虾帮忙，多谢！！

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