Data, Graph Analysis on the GRE Math Test — Practice Questions
The GRE Math test contains some questions that first ask you to study data in a chart or graph, and then answer questions based on that data.
In the following practice questions, you need to refer to the supplied graphs to calculate the annual cost of electricity for an average household, and then one family’s savings based on their investment in a geothermal furnace and extra insulation.
Practice questions
The following questions are based on these graphs. (Note: the graphs are drawn to scale.)

Assuming the average household uses 15 kilowatthours (kWh) of electricity per day to heat its home, approximately how much would the average household pay for electricity per year if located in the northeast region?
A. $1,500
B. $1,800
C. $2,200
D. $2,700
E. $3,200

The Joneses live in the north central region. After paying a whopping $4,500 on electricity last year, they installed a new geothermal furnace and extra insulation at a cost of $8,000 total, which cut their heating bill by 35%. At this rate, about how many years will it take them to recoup their investment?
A. 16
B. 12
C. 8
D. 6
E. 3
Answers and explanations

D
If 15 kWh represents 30 percent of the family’s total daily electricity usage, the total daily usage would be 0.30x = 15 kWh;
At $0.15 per kWh in the northeast, that’s a daily cost of $7.50. Multiply $7.50 by 365 days for an annual electricity cost of $2,737.50, or approximately $2,700.

A
In this problem, $4,500 represents the family’s total electric bill. Heating alone represents 30% of that, or $4,500 times 0.30, which equals $1,350. Cutting the heating bill by 35% saves them $1,350 times 0.35, which is $472.50, which is pretty close to $500 per year in savings. And $8,000 divided by $500 is 16 years; actually, the number of years to recoup the investment is somewhat more than that due to rounding $472.50 up to $500.