Arithmetic mean: grouped data
		Money Income of Households, 1998 (in 1,000’s)
				Household $												f							Midpoint
					< $10,000									10,705											5,000
			$10,000-14,999												8,093									12,500
			$15,000-24,999											14,587										20,000
			$25,000-34,999											13,698										30,000
			$35,000-49,999											16,660										42,500
			$50,000-74,999											19,272										62,500
						$75,000+								20,860										75,000
													103,875
	Source:  U.S. Census Bureau, Statistical Abstract of the U.S., 2000, Table 738.