prep两道数学题求解！快考试了~求NN~

faye720

1、The rate of a certain chemical reaction is directly propotional 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 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%increse
答案是D  
题目的问题也没太读懂，求NN解答

2、At a speed of 50m/h,a certain car uses 1 gallons of gasoline every 30 minutes.If the car starts with a full 12 gallon tank of gasoline and travels for 5 hours at 50m/h.the amount of gasoline used would be what fraction of a full tank?
A.3/25    B.11/36   C.7/12   D.2/3    E.25/30
答案是E,我算出来是D。求解

jeanq

第一题 与A平方成正比与B成反比 即A^2/B
          当B增加100%，要使原数不变，则A变成根号2倍， 即增加40%

jeanq

第二题 5小时用了2×5*1=10galon 10/12=25/30