问一道prep上的数学题

conanlan

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 chemical B present. If the concentration of chemical B is increased by 100%, which of following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged

answer: 40%decrease

这究竟是怎么整出来的呢？！

还有就是再DS中如果条件证明结论不正确，算不算对呢？！

比如问a》2么？

然后给出的两个条件有一个是a《0，那这个条件要选么？！

formcardiff

如果DS中得到的结果与结论相反，也就是说可以确定结论不正确，这样也算是正确答案。

比如：问X＜3？通过条件一和二得出的结果是X＞3，那么就选C