继续向NN们请教prep数学题。。~ 拜谢!

挞兜

1.The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemica A present and inversely proportional to the concentration of chemical B present. If the concentration of chemical B is increased by 100 persent, which of the following is closest to the perchent change in the concentration of chemical A required to keep the reaction rate unchanged?
 答案是：40%  increase.
请nn们解答的时候顺路解释下题目意思呀。。。表示完全被绕晕了。。。

2.At a dinner party, 5 people are to be seated around a circular table. 2 seating arrangements are considered different  only when the positions of the people are different relative to each other .What is the total number of different possible seating arrangements?
答案：24.。

3.DS.
r,w,b,r, are all integers, is r/(b+w+r) larger than w/(b+w+r)?    
a. r/(b+w) > w/(b+r)
b.b-w> r
答案是A。。

以上，请NN们不吝赐教啦~~  谢谢！~

挞兜

嗯~~   虽然模考总是很伤感。。但是。。。  考试是拼rp的！！~~~  

biabia123

大家一起加油，一战成功~~

挞兜

12.6一战啊。。。

-- by 会员 biabia123 (2011/12/4 10:43:25)

握手！！   我也是啊！！！

biabia123

12.6一战啊。。。

挞兜

噢！！  是这个答案没有错！~~  谢谢LS了呀！！~~~   话说在做prep的话，亲莫不是也快考试了？~

biabia123

外面大圆的面积是πr^2
里面小圆的面积是π（r-s）^2
大圆面积减小圆面积就是那个metal frame的面积：πr^2-π（r-s）^2=πs(2r-s)
lz自己去算下，应该是这个答案

挞兜

呃。。。了解了。~   但是。。我还是不知道答案怎么来的。。

biabia123

lz，那个s指的是metal frame的宽度，就是图上那个灰色环状的宽度，不是里面那个小圆的半径，我昨天也做过这题的~

挞兜

嗷。。。求指导啊求指导。。~~~