求prep数学一道

kudoucliff

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 percent, which of the following is closest to the percent change 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
答案是D……看来我没有读懂题啊……

wenjie87

由提议可知，设K=A^2/B
如果B增加了100，要保持K不变，A要改变多少？设A的改变量为X
K=A(1+X)^2/B(1+100%)
要使得K不变，则需要（1+X)^2=2
解得X为0.414

kudoucliff

谢谢！懂了：-）