Add the same amount to both numbers — the gap, and the answer, never change
Equal-Addition Balance — subtract a 7, 8 or 9 without borrowing.
For 163 − 47: 47 needs +3 to reach 50, so add 3 to both numbers → 166 − 50 = 116. The gap between them is unchanged, so the answer is too — and there is no borrow. You enter the method step by step — the +k, both rewritten numbers, then the subtraction — and each step unlocks only when the one before it is right. Five levels climb from 2- to 3-digit; the steps fade away as you climb until only a bare answer box is left, and a short timed boss caps each level.