Fast arithmetic you can do in your head. Start with small numbers (L1) and work up to large-scale mental calculations (L5). No pen needed.

Business calculations with clean, manageable numbers. Levels 1–3 are mental. Levels 4–5 are harder — use pen and paper if needed.

The 20 key metrics every consultant needs cold. Levels 1–3: mental. Levels 4–5: pen & paper recommended. Covers profit, margins, ROI, NPV, CAGR, market share & pricing.

Grocery bills, restaurant tips, discounts, fuel, splitting bills — the mental math you actually use every day.