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Opens on Chapter 6’s example: the piano tuners of Marlow, an invented city of 800,000.
Enter your numbers, then press Calculate.
From the book, Chapter 6. 800,000 people ÷ 2.5 = 320,000 homes; one in 20 with a piano is 16,000; tuned once a year, shared among tuners who each do 4 a day for 250 days (1,000 a year): about 16 tuners. Joaquin’s first route: 300 × 2.5 × 6 = 4,500 tacos a week. Every factor is an assumption to say out loud.
Rounding is half up, the way the book rounds. Numbers can be typed as 1,450, $38, 12%, 1/20, 2.5 million or 3 × 10⁷. Everything stays in your browser: no sign-up, nothing stored or sent.