prep数学疑问一题~

 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 present, 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

B increase by 100 percent --> 对整个rate 的影响是除以2

为了保持rate不变

A的平方的值就得double

(A(1+r))^2 = A^2 * 2

r=根号二的约数0.4

选D

嗯~明白了~~谢谢LS`~