1. 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
Answer: D
题目什么意思啊？没看懂~~
2. If x is positive, which of the following could be the correct ordering of 1/x, 2x, and x^2 ?
I) x^2 <2x<1/x
II) x^2 <1/x<2x
III) 2x<x^2 <1/x
(A) None
(B) I only
(C) III only
(D) I and II only
(E) I , II and III
Answer: D
请问这种题目一般要考虑那几个方面才能保证不会漏掉任何情况啊？
3. If x is a positive number less than 10, is z greater than the average (arithmetic mean) of x and 10 ?
(1) On the number line, z is closer to 10 than it is to x.
(2) z = 5x Answer:A 4. A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture that was 5 percent gravel G, by weight. What is the value of x ? (1) y = 10 (2) z = 16 Answer: D 怎么算出来的呢？我选择c Answer: D 怎么算出来的呢？我选择c
Answer:A
4. A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture that was 5 percent gravel G, by weight. What is the value of x ?
(1) y = 10
(2) z = 16 Answer: D 怎么算出来的呢？我选择c
Answer: D
怎么算出来的呢？我选择c
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