菜鳥小妹求思路~~~~~~~~~~~~~~~

hijenny

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d







If the speed of x meters per second is equivalent to the speed of y kilometers per hour, what is y in terms of x ?



(1 kilometer = 1,000 meters)



(A) 5x/18

(B) 6x/5

(C) 18x/5

(D) 60x

(E) 3,600,000x
答案c
要如何換算 我算出來e 這種題型是我的比較弱的

好好备考Gmat

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?

y=ka^2/b
b'=2b
y'=ka'^2/b'
若要y=y'
则ka^2/b=ka'^2/b'
  ka^2/b=ka'^2/2b
  a^2=a'^2/2
  a'^2=2a^2
  所以a'=2^1/2 a
2^1/2=1.4
选变化40%

tkrayla

把y km/h换成m/s=>y*1000/3600=5y/18 m/s=x m/s
=>5y/18=x=>y=18x/5