Sat practice Test #8 Answer Explanations

Choice D is correct. The number 3.39 in the equation y = 3.39x + 46.89 
is the slope, which is the change in y per unit change in x. Because 
y represents the amount of plastic produced annually, in billions of 
pounds, and x represents the number of years since 1985, the number 
3.39 represents the rate of change of the amount of plastic produced 
with respect to time, in units of billions of pounds per year. The 
change is an increase since 3.39 is positive, and it is described as an 
average change because the data show increases that are sometimes 
more and sometimes less than 3.39.

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Choice A is incorrect. It is the interpretation of the number 46.89 in 
the line of best fit equation, y = 3.39x + 46.89. Choices B and C are 
incorrect because they are expressed in the wrong units. The number 
3.39 has units of billions of pounds per year, but choice B has units of 
years and choice C has units of billions of pounds.
QUESTION 22
Choice A is correct. Since x is the number of years since 1985,
the year 2000 corresponds to x = 15 and the year 2003 corresponds
to x = 18. The corresponding points on the line of best fit are 
approximately (15, 98) and (18, 107). This means that approximately 
98 billion pounds of plastic were produced in 2000 and approximately 
107 billion pounds of plastic were produced in 2003. To calculate the 
percent increase, subtract the amount of plastic produced in 2000 
from the amount of plastic produced in 2003 and then divide the result 
by the amount of plastic produced in 2000 and multiply by 100. This 
yields
( 
107 − 98 
_
98 
)
∙ 100 = 9.2, or approximately 10%.
Choices B and C are incorrect and may be the result of misreading the 
graph or making an arithmetic error. Choice D is incorrect and may be 
the result of approximating the amount of plastic produced, in billions 
of pounds, in the year 2003 (x = 18).
QUESTION 23