Grow by Numbers

Who it is for

• Adults who want the math they missed, taught through something that pays them back the same month: every idea is used on the shelf the week you learn it.
• Households that want to grow some of their own food: a shelf that cuts greens every three days, with the seed, the light and the cost worked out first.
• A gift for a teen of 13 or older, with an adult alongside for the shelf, the lights and the money.
• Homeschool, maker and allotment families who want a project with a number at the end of every step.

Not for: exam-syllabus coverage or proofs, or anyone who wants the shelf without the arithmetic. It is never a substitute for an electrician or a food-safety officer where the book says so.

What you build: the Microgreen Shelf

One wire shelf, four tiers, 8 trays, one 40 W LED bar a tier. Every chapter hands it one number.

• The calendar: two trays every 3 days, radish, broccoli, sunflower and pea in turn. In the first 30 days, 10 sowings and 7 harvests, about 4,370 g cut; then about 1,406 g (3.1 lb) a week, and never more than 8 trays on the shelf.
• The growth: radish multiplies its seed weight about ×10 in 9 days, 1.29 a day; the S-curve says one more day would add only about 11 g.
• The light and the cold: 2.56 kWh a day; cut greens at 5 °C (41 °F), planned for 7 days, no pack older than 6.
• The business, if you choose it: about 3.54 to grow a tray, 2 oz packs at 5, and break-even on the 324 kit after 16 trays sold, about 7 weeks of the surplus. These are worked examples at illustrative October 2026 prices, with a column for your own numbers, not promises.

The game: every chapter ends with Call It (write the number before you measure) and Check It (the gap scores 3, 2, 1 or 0). A Quest Map tracks the eleven stations, the first eight trays earn a Harvest Score of Gold, Silver or Bronze, and a Trophy page holds the result. 12 more crops are worked out on the Crop Shelf.

The shelf was worked out on paper from published figures, not grown by us: weigh and measure your own. The book was written in collaboration with AI tools and reviewed by the author. Its numbers are checked by a verification program, and its figures are drawn by the same program, but mistakes may remain: see corrections & errata. LED lights and water share a shelf: plug-in only, through a GFCI (US) or RCD (UK) outlet. Selling food has rules where you live; the book names them and says when to ask.