GRE Sample Test 4 Quantitative Reasoning 1

To find the per capita, or per person, personal energy use in Country Y in 2005, divide the personal energy use by the number of people. Since the question gives you the population—500 million people—you only need to find the personal energy use.
According to the top graph, total energy use in 2005 was about 675 million kilowatt-hours. According to the bottom graph, personal energy use was about 20% of the total, or 675 × 0.20 = 135 million kilowatt-hours. Divide this number by the population of Country Y in 2005: 135 million kilowatt hours divided by 500 million people = 0.27 kilowatt-hours per person, or choice (C).