1.c. The average president is 55 years, 117 days old on his first Inauguration Day. On Jan. 20, Barack Obama will be 47 years, 169 days old; John McCain will be 72 years, 144 days old. The extremes: Ronald Reagan was 69 years, 348 days old when he was first inaugurated; Theodore Roosevelt was 42 years, 322 days old when he took office.
2.b. 5 feet 10. Obama is 6 feet 1; McCain is 5 feet 7. The extremes: Abraham Lincoln was 6 feet 4; James Madison was 5 feet 4.
3.c. The exact average is 3.7 biological children (2.1 sons, 1.6 daughters). Obama has two daughters; McCain has four biological children (two sons and two daughters) and three adopted children (two sons and one daughter).
4.c. When they took office, 24 presidents had no living parents. Obama falls into this category (though if elected, he could be the first president with a living grandparent, Madelyn Dunham. McCain's 96-year-old mother, Roberta, is still living.
5. c and d. Six presidents were named James (Madison, Monroe, Polk, Buchanan, Garfield and Carter) and five were named John (both Adamses, Tyler, Kennedy and Coolidge, who was known by his middle name, Calvin).
6.d. On average, presidents are five years, 16 days older than their wives. Obama is two years, 166 days older than Michelle Obama; McCain is 17 years, 264 days older than Cindy McCain. The greatest age differential was between Grover Cleveland and his wife, Frances: 27 years, 125 days.
7.c. 29. Only four were career military men and they all rose to the rank of general: (William Henry Harrison, Zachary Taylor, Ulysses S. Grant and Dwight D. Eisenhower). Obama has never served in the military; McCain rose to captain in the Navy before his retirement.
8.b. Twenty-two of the 42 presidents had fathers who farmed or were landowners, ranging from hardscrabble spreads to estates with slaves. The most recent were Lyndon B. Johnson and Jimmy Carter. McCain's father was an admiral in the Navy; Obama's was an economist.
9.b. Twenty-one of the 42 presidents were lawyers before becoming president. Obama is a lawyer; McCain is not.
10.b. Five presidents were widowed and then remarried, and one (Reagan) divorced his first wife. John Tyler, Benjamin Harrison and Woodrow Wilson's first wives all died while they were president. Millard Fillmore's first wife died a month after he left office (she caught cold at his successor's inaugural). Theodore Roosevelt's first wife died four years after they were married, long before he got into politics. (Andrew Jackson is an anomaly: He was married twice but to the same wife, because her divorce hadn't gone through the first time.) Obama's wife is his first; McCain divorced his first wife.
11.c. Twenty-three of the 42 presidents were related to at least one other. They range from thetwo father-son pairs (John Adams and John Quincy Adams; George H.W. Bush and George W. Bush) to Madison and Taylor (who were second cousins) all the way to John Quincy Adams and Benjamin Harrison (who were 22nd cousins once removed) and John Quincy Adams and George W. Bush (who are 20th cousins three times removed). According to the New England Historic Genealogical Society, Obama is a cousin to at least five presidents (Madison, Harry Truman, Lyndon B. Johnson, Gerald Ford and George W. Bush -- the closest would be Madison, a third cousin, nine times removed, and LBJ, a fourth cousin, three times removed), and McCain has no presidential relatives. The most "related" president is George W. Bush, who is the son of one president and the cousin of six others.
Ian Randal Strock is the author of "The Presidential Book of Lists," which will be published next week. He is also the editor of SFScope and blogs about presidents at uspresidents.livejournal.com.