while the number in parentheses shows the percentage of the total population comprised by that age group.

Year Total Population 19 and Under

20–64 years

Over 65

1970 205.0 million

77.2 (37.6%)

107.7 (52.5%) 20.1 (9.8%)

2000 275.4 million

78.4 (28.5%)

162.2 (58.9%) 34.8 (12.6%)

2030 351.1 million

92.6 (26.4%)

188.2 (53.6%) 70.3 (20.0%)

TABLE A4 U.S. Age Distribution, 1970, 2000, and 2030 (projected)

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A • The Use of Mathematics in Principles of Economics 511

FIGURE A6 Pie Graphs of the U.S. Age Distribution (numbers in millions) The three pie graphs illustrate the division

of total population into three age groups for the three different years.

In a pie graph, each slice of the pie represents a share of the total, or a percentage. For example, 50% would be

half of the pie and 20% would be one-fifth of the pie. The three pie graphs in Figure A6 show that the share of
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