请教一道pp题，快考了。急。。

irinamm · 发表于 2006-7-11 14:57:00

The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of the chemical B present . If the concentration of chemical B is increased by 100 persent, which of the following is closest to the percent change in the concentration of chemical of A required to keep the reaction rate unchanged?

A 100% increase

B 50% decrease

C 40% decrease

D 40 % increase

E 50% increase

不太懂

mba06 · 发表于 2006-7-11 15:03:00

i choose B

rate = p * A^2 / B, p is a constant.

B is doubled, and A is remain constant. So rate is 50% decreased.

helenying · 发表于 2006-7-11 15:11:00

选d,算式跟楼上的一样,但是结果接近d

helenying · 发表于 2006-7-11 15:14:00

选d,算式跟楼上的一样,但是结果接近d

helenying · 发表于 2006-7-11 15:15:00

因为是a的平方,

mba06 · 发表于 2006-7-11 15:18:00

昏了﹐多謝指正。題目都沒看清就選答案了。D

irinamm · 发表于 2006-7-11 15:45:00

谢谢！！

这道呢？？

The distribution of a survey has a mean of 21 and a standard deviation of 6. A number is between 1 and 2 standard deviations below the mean .which could be the number?

30,20,18,12,6??

题目不太懂A number is between 1 and 2 standard deviations below the mean？？

请教

mba06 · 发表于 2006-7-11 16:04:00

一個standard deviation就是6﹐兩個就是12。一個standard deviation below mean就是 21 -6﹐ 二個就是 21 - 12﹐看看那個合適。

xiaochun624 · 发表于 2008-10-26 01:40:00

以下是引用mba06在2006-7-11 15:03:00的发言：

i choose B

rate = p * A^2 / B, p is a constant.

B is doubled, and A is remain constant. So rate is 50% decreased.

题目问的好像不是这个吧。

问题是：在保持Rate不变的情况下，A该如何变化？

B Double了，A'^2=2A => A'=1.41A (2开根号）=>A'增加了接近40%

请教一道pp题，快考了。急。。

请教一道pp题，快考了。急。。

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