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Best Guess · Puzzle #9 · Thursday, October 8

Best Guess: the answers

Four questions, each with one true number. Here they are with their answers, how to reason each one out, and where the number comes from. Play today's Best Guess.

  1. 1. How many public library outlets (central libraries, branches, bookmobiles) are there in the 50 states and DC?

    The answer: 17,351. They belong to about 9,200 separate public library systems.

    Napkin math
    1. 330Mpeople in the US
    2. ÷15kpeople to a library

    ≈22klibrary outlets

    Source: Institute of Museum and Library Services, Public Libraries Survey Fiscal Year 2023: Data File Documentation

  2. 2. How many gallons of milk did Americans drink in 2021?

    The answer: about 5.2 billion. Americans drink far less milk than they used to: availability has been falling for decades.

    Napkin math
    1. 330Mpeople in the US
    2. ×365cups each a year (one a day)
    3. ÷16cups to a gallon

    ≈7.53Bgallons

    Source: USDA Economic Research Service, Food Availability (Per Capita) Data System: Dairy (fluid milk), per capita gallons

  3. 3. How many times a year does the average person flush a toilet at home?

    The answer: about 1,825 flushes. Flushing is the biggest indoor use of water in single-family homes, and the average flush fell from 3.65 to 2.6 gallons between the two national studies.

    Napkin math
    1. 6flushes a day
    2. ×365days a year

    ≈2,190flushes

    Source: Water Research Foundation, Residential End Uses of Water, Version 2: Executive Report (2016)

  4. 4. How many times does the average person's heart beat in a lifetime?

    The answer: more than 2.6 billion. That's about 100,000 beats every day, Cleveland Clinic says.

    Napkin math
    1. 70beats a minute
    2. ×60minutes an hour
    3. ×24hours a day
    4. ×365days a year
    5. ×80years in a lifetime

    ≈2.94Bheartbeats

    Source: Cleveland Clinic, Fun Facts About Your Heart

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