[求助]一道PREP模拟试题，题目看不大明白，请牛牛帮忙解一下

annika_shao

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

A) 100% decrease

B) 50% decrease

C) 40% decrease

D) 40% increase

E) 50% increase

做PREP时遇到的题目，觉得题目理解不了。请大家指点解题思路。

meggie_xm

选择D吗？我理解是b引起的下降要a上升多少来使其不变。你看对不对？

mba1688

the reaction rate 和A的平方.B的倒数成比例.现在是B增加了100%,问A如何变化才能保证the reaction rate unchanged

由此可知道A必须变成40% increase,所以选D

annika_shao

能不能有更详细的解？就是怎么算出最后答案的。我的数学实在是。。。

howga

设：Y=A²/B

B increased by 100%=2B

假设A增加的比例是X，那么A(1+X)²/2B=A²/B

即(1+X)²=2，X=0.41左右，所以选D

annika_shao

终于理解了，多谢，多谢

WELCOME1

OK

dicer9

谢谢楼主和大家 今天也碰到这题 现在懂了~