三道 PP 求教~~

1.
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 x 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

請問如何計算呢 謝謝

2.
The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A persent 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

3.
In a survey of students, each student selected from a list of 12 songs the 2 songs that the student like best. If each song was selcetd 4 times, how many students were surveyed?

A.  96
B.  48
C.  32
D.  24
E.  18

Answer : D

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