Douglas Hofstadter's Innumeracy Exercises (Solutions)

It took me a few hours to complete these rough solutions, without any references. I am not entirely confident in their accuracy. It might be fun to compare solutions, though, and hopefully my thought process will be helpful in at least a few places.

  1. What's the gross state product of California? (10: 10-100 billion)
  2. How many people die per day on Earth? (6: 1-10 million)
  3. How many traffic lights are there in New York City? (a few hundred streets squared should give an upper bound to the intersections, so 4: 10-100k)
  4. How many Chinese restaurants are there in the U.S.? (4, which would work out to a few thousand in each state)
  5. How many passenger-miles are flown each day in the U.S.? (100k's of travelers * 100's of miles = 5 + 2)
  6. How many volumes are there in the Library of Congress? (tens of millions = 7)
  7. How many notes are played in the full career of a concert pianist? (a page of music has probably 10 bars, each of which has 10-100 notes (3); concert pianist probably plays 100s of pages of music a day (2); plays every day a year (2); plays tens of years (1); add the exponents: 8... hundreds of millions)
  8. How many square miles are there in the U.S.? How many of them have you been in? (1,000 x 1,000 = 3 + 3 = 6; not sure what he means by "been to," but I probably occupy a square foot, travel a few thousand (effectively unique) square feet a day (so < 10 miles), and have lived for more than 8,000 days: say 4, to account for driving/flying)
  9. How many syllables have been uttered by humans since 1400 A.D.? (100m people * a few thousand words a day (so, 10k+ syllables) * hundreds of years * hundreds of days = 8 + 4 + 2 + 2 = 16)
  10. How many "300" games are bowled in the U.S. per year? (probably 100-1,000, so 2)
  11. How many stitches are there in a stocking? (I have no idea how these things are woven, or what constitutes a "stitch," but as a wild guess, maybe a 100k or so: 5)
  12. How many characters does one need to know to read a Chinese newspaper? (I've heard about 10,000)
  13. How many sperms are there per ejaculate? (Douglas! A few million?)
  14. How many condors remain in the U.S.? (What's a condor? A few hundred?)
  15. How many moving parts are in the Columbia space shuttle? (I doubt that very many parts move, maybe a few thousand little guys?)
  16. How many people in the U.S. are called "Michael Jackson"? "Naomi Hunt"? (high 100ks for "Michael"s (5), maybe 70% born late enough for "Thriller" to do anything (low 5), then probably a 1% shot of having the name... so a few thousand? "Naomi Hunt" might be a full order of magnitude lower, giving 100 or so)
  17. What volume of oil is removed from the earth each year? (hundreds of millions of barrels? Maybe I should read the news...)
  18. How many barrels of oil are left in the world? (my last answer * < 100 years left: billions of barrels? 9)
  19. How much carbon monoxide enters the atmosphere each year in auto exhaust fumes? (sensing an agenda here... 100s of millions of cars, 10-100lbs each a day? 9)
  20. How many meaningful, grammatical, ten-word sentences are there in English? (the Q is ten words, too, not surprisingly... this is a hard one. Suppose there are 100k-1m common words, then 10 spots gives (100k-1m)^10, or 5 * 10 = 50 on the big scale. But the odds are pretty low it's grammatical, or meaningful, which might bring you way down, especially since each word has a chance of ruining the whole thing. Say, 10 independent chances to screw things up, at a .1% success rate each time, so the odds of a success are (1/1000)^10 or -30. Gives us 20 for the final answer)
  21. How long did it take the 200-inch mirror of the Palomar telescope to cool down? (I imagine things cool down at a decreasing rate, and that things with a high surface area cool down faster... maybe a few days?)
  22. What angle does the earth's orbit subtend, as seen from Sirius? (10-100 degrees?)
  23. What angle does the Andromeda galaxy subtend, as seen from earth? (1-10 degrees?)
  24. How many heartbeats does a typical creature live? (say, about one a second... 60 seconds * 60 minutes * 24 hours * 365 days * 20 years = 6, a few million)
  25. How many insects (of how many species) are now alive? (vaguely recall hearing "trillions of insects," maybe 100m's * 10k's of species?)
  26. How many giraffes are now alive? Tigers? Ostriches? Horseshoe crabs? Jellyfish? (5, 5, 5, 7, 8)
  27. What are the pressure and temperature at the bottom of the ocean? (10k times the surface? 100 times cooler?)
  28. How many tons of garbage does New York City put out each week? (10s of millions of people * 10 pounds a week = 100 million pounds/1,000 lbs per ton = 5)
  29. How many letters did Oscar Wilde write in his lifetime? (5-10 a day * 365 * 35 (?) = 4, 10k)
  30. How many typefaces have been designed for the Latin alphabet? (thousands?)
  31. How fast do meteorites move through the atmosphere? (100k miles per hour? no idea)
  32. How many digits are in 720 factorial? (say, each of 10 * 11 * 12 * ... * 99 in the product contributes a digit, and each of 100 * 101 * ... * 720 contributes 2, for a total of 711 digits... so, 3)
  33. How much is a brick of gold worth? ($10k?)
  34. How many gold bricks are there in Fort Knox? How much is it worth? (I'll work backwards: a few hundred billion / 10k = 11 - 4 = ten million bricks?)
  35. How fast do your wisdom teeth grow (in miles per hour, say)? (to be generous, maybe an inch in 20 years.. then, do some dimensional analysis to give -7 (on the exponent scale))
  36. How fast does your hair grow (again in miles per hour)? (one inch in 20 days? cuts off two orders of magnitude, -5)
  37. How fast is Venice sinking? (a foot every 1,000 years?)
  38. How far is a million feet? A billion inches? (America is probably 2,000 * 5,280 ft wide, say 3 + 4, or ten million feet; so maybe the width of Texas? a billion inches is 7 - 1 + 3 = 2 orders of magnitude more, or about 100 million feet... say, two times around the globe?)
  39. What is the weight of the Empire State Building? Of Hoover Dam? Of a fully loaded jumbo jet? (a million tons? 10 million? 100?)
  40. How many commercial airline takeoffs occur each year in the world? (100k passengers / 100s on a flight = 1,000s flights a day = 3 + 2 = 5... probably 6 because 5 seems low)

Here are my answers in raw format, in case anyone is interested in processing collective results.