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Price tags · Puzzle #7 · Tuesday, October 6

Price tags: 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 Price tags.

  1. 1. A year with a Lab: What does ASPCA Pet Health Insurance estimate a medium-size dog, like a Labrador, costs a year in food, care and supplies?

    Photo: Skansken, CC BY 3.0
    Not counted
    One-time costs like a crate and spaying

    The answer: about $669. Small dogs came in around $512 a year and large dogs around $1,040.

    Napkin math
    1. 12months a year
    2. ×$50a month on food, treats and checkups

    ≈$600

    Source: ASPCA Pet Health Insurance, How Much Does It Cost to Have a Dog?

  2. 2. Duolingo: How much did Duolingo learners spend on the app (total bookings) in 2025?

    Paid subscribers
    12.2 million at the end of 2025

    The answer: about $1.16 billion. Duolingo's bookings grew 33% in 2025, from $870.6 million the year before.

    Napkin math
    1. 10Msubscribers paying
    2. ×$8each a month
    3. ×12months a year

    ≈$960M

    Source: Duolingo, Inc. (SEC Form 8-K, Exhibit 99.1), Q4 2025 Shareholder Letter

  3. 3. 1962 Ferrari 250 GTO: What did a 1962 Ferrari 250 GTO (chassis 3413) sell for at RM Sotheby's Monterey auction in August 2018?

    Photo: Lothar Spurzem, CC BY-SA 2.0 de
    What
    The third of only 36 Ferrari 250 GTOs built
    Sold
    RM Sotheby's, Monterey, California, 2018

    The answer: $48.4 million. RM Sotheby's billed it as the world's most important, desirable and legendary motor car.

    Napkin math: Only 36 exist and collectors call it the holy grail of cars, so a public sale could reach tens of millions.

    Source: RM Sotheby's, 1962 Ferrari 250 GTO by Scaglietti | Monterey 2018

  4. 4. A light bulb left on: At the US average electricity price in August 2026, what would it cost to leave one 60-watt light bulb on for a whole year?

    Photo: Gauravggs, CC BY-SA 4.0
    Bulb
    an old-style 60-watt incandescent

    The answer: about $103. An LED bulb that gives the same light uses a fraction of the power.

    Napkin math
    1. 60watts
    2. ×9,000hours in a year
    3. ÷1,000watt-hours in a kilowatt-hour
    4. ×$0.15a kilowatt-hour

    ≈$81

    Source: Federal Reserve Bank of St. Louis (FRED), from the US Bureau of Labor Statistics, Average Price: Electricity per Kilowatt-Hour in U.S. City Average

All of puzzle #7 · The archive