SOS!!! PREP数学题求教~~

rainzyx23 · 发表于 2011-6-7 09:46:06

连做三套PREP模考死活要把数学51做出来！！可是三套全都是50.。。难道这就是我的真实水平嘛。。。不甘。。。为啥觉得PREP的数学还有挺有难度的的？实战比这个简单还是难呢？呜呜。。明天就要考了。。如果数学不上51，很难770的呀~~~
废话少说，上题！

1. A certain city with a population of 132,000 is to be divided into 11voting districts, and no district is to have a population that is more than 10 percent greater than the population of any other district. What’s the minimum possible population that the least populated district could have?答案是１１０００。

2.The rate of a certain chemical reaction is directly proportional tothe square of the concentration of chemical A present and inverselyproportional to the concentration of chemical B present. If the concentrationof chemical B is increased by 100 percent, which of the following is closest tothe percent change in the concentration of chemical A required to keep thereaction rate unchanged?
答案40% increase ~求教！

小楼独醉 · 发表于 2011-6-7 10:01:40

这题好难啊，不会做，同问

courtdancer · 发表于 2011-6-7 10:14:11

连做三套PREP模考死活要把数学51做出来！！可是三套全都是50.。。难道这就是我的真实水平嘛。。。不甘。。。为啥觉得PREP的数学还有挺有难度的的？实战比这个简单还是难呢？呜呜。。明天就要考了。。如果数学不上51，很难770的呀~~~
废话少说，上题！

a certain city with a population of 132,000 is to be divided into 11voting districts, and no district is to have a population that is more than 10 percent greater than the population of any other district. What’s the minimum possible population that the least populated district could have?
答案是１１０００。

-- by 会员 rainzyx23 (2011/6/7 9:46:06)

假设11个区从小到大排列为a1,a2,a3,...a11
即a1<=a2<=...<=a11
那么按照题意，a11<=a1(1+10%)
同理a10,a9,...a2<=a1(1+10%)
不等式左边右边分别相加为
a2+a3+...+a11<=a1(1+10%)*10
a1+a2+...+a11=132000
所以
132000-a1<=11a1
a1>=11000

camelo777 · 发表于 2011-6-7 10:16:16

LS好强...

rainzyx23 · 发表于 2011-6-7 10:18:55

谢谢！解释得很清楚~~~第二道题不知道有没有解释？

courtdancer · 发表于 2011-6-7 10:27:06

谢谢！解释得很清楚~~~第二道题不知道有没有解释？

-- by 会员 rainzyx23 (2011/6/7 10:18:55)

上班....
稍等...

wallstreeter · 发表于 2011-6-7 10:30:44

Rate=kA2*d/B
k,d常数；AB分别是两个浓度
B变成了2B。。。
为保证R不变，A就得乘根号2
也就是1.414倍A

rainzyx23 · 发表于 2011-6-7 10:34:11

原来此题这么简单。。。谢谢你！！！

rainzyx23 · 发表于 2011-6-7 10:35:28

Rate=kA2*d/B
k,d常数；AB分别是两个浓度
B变成了2B。。。
为保证R不变，A就得乘根号2
也就是1.414倍A

-- by 会员 wallstreeter (2011/6/7 10:30:44)

谢谢你！原来是这个意思。。inversely proportional就是负相关的意思是吗？

wallstreeter · 发表于 2011-6-7 10:43:08

Rate=kA2*d/B
k,d常数；AB分别是两个浓度
B变成了2B。。。
为保证R不变，A就得乘根号2
也就是1.414倍A

-- by 会员 wallstreeter (2011/6/7 10:30:44)

谢谢你！原来是这个意思。。inversely proportional就是负相关的意思是吗？

-- by 会员 rainzyx23 (2011/6/7 10:35:28)

我理解是“成反比” 呵呵客气

SOS!!! PREP数学题求教~~

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