■ Principle 2: Don’t confuse percentages, averages, and numbers. Question
1 asks you to determine which year had the greatest percent change from
the previous year. You should first recognize that the years with the greatest
absolute change from the previous year were 2003 and 2010. You may then be
tempted to select 2010 since the absolute difference between 2009 and 2010
is greater than the absolute difference between 2003 and 2004. But recall
from the percentages chapter that percent change depends on the original
value. Since the revenue in 2003 is so much less than the revenue in 2009,
the percent change from 2003 might be greater than from 2009, even though
the absolute change is less. Thus you should calculate the percent change for
those two periods (keeping in mind the importance of estimating!):
Percent change from 2003 to 2004: The revenue in 2003 is roughly $37
million and the revenue in 2004 is roughly $64 million. The percent
change is thus: 62 – 37 37 = ≈0.68 = 68%.
Percent change from 2009 to 2010: The revenue in 2009 is roughly $75
million and the revenue in 2010 is roughly $44 million. The percent
change is thus 75 – 44 75 = ≈0.41 = 41%. Thus the correct answer for Question
1 is B.
■ Principle 3: Use your eye. Unless noted otherwise, the diagrams are drawn
to scale. This is helpful since you can minimize calculations when you are
comparing choices or elements of a graph. For example, in Question 2, you
can determine all of the correct answers by eyeballing instead of by doing
calculations:
Choice A: In the second graph, the percentage revenue from computers
in 2004 is about equal to the percentage revenue from computers in 2003.
From the first graph, you know the total revenue in 2004 was greater than
in 2003. Thus the revenue from computers in 2004 is an equal slice of a
larger whole (relative to 2003). → Keep Choice A.
Choice B: In the second graph, the percentage revenue from computers in
2005 is slightly less than the percentage revenue from computers in 2004.
From the first graph, you know the total revenue in 2005 was less than
in 2004. Thus the revenue from computers in 2005 is a smaller slice of a
smaller whole (relative to 2004). → Eliminate Choice B.
Choice C: In the second graph, the percentage revenue from computers
in 2006 is greater than the percentage revenue from computers in 2005.
From the first graph, you know the total revenue in 2006 was greater than
in 2005. Thus the revenue from computers in 2006 is a larger slice of a
larger whole (relative to 2005). → Keep Choice C.
Choice D: In the second graph, the percentage revenue from computers in
2008 is roughly equal to the percentage revenue from computers in 2007.
From the first graph, you know the total revenue in 2008 was less than
in 2007. Thus the revenue from computers in 2008 is an equal slice of a
smaller whole (relative to 2007). → Eliminate Choice D.452 PART 4 ■ MATH REVIEW04-GRE-Test-2018_313-462.indd 452 12/05/17 12:07 pm