Add the biggest place first — no carries to hold
Left-to-Right — add (or subtract) the big places first.
Flip the schoolbook method: 54 + 38 → 50 + 30 = 80, then fold in the ones: 80 + 12 = 92. For subtraction, let a place go negative and adjust (83 − 47 → 40, then −4 → 36). You enter the method step by step — the running total after each place is folded in, biggest place first — and each step unlocks only when the one before it is right. Six levels climb from 2-digit up to 8-digit numbers; the steps fade away as you climb until only a bare answer box is left.