⚔️ Swipe through the fruit with the correct answer!
20以內退位減法（例如 13-5）是不少小朋友的絆腳石，關鍵策略是「破十法」：先由13減3到10，再減2，答案是8。另一個思路是「想加算減」：13-5，就是想「5加多少等於13」。Ninja Slice 用爽快的切割動作，讓這些必須的反覆練習變得不枯燥。
Borrowing subtraction within 20 (e.g. 13−5) trips up many children. The key strategy is "break ten": subtract 3 from 13 down to 10, then subtract 2 more to get 8. Another route is "think addition": 13−5 means "5 plus what makes 13?" The ninja's satisfying slicing turns these essential repetitions into fun.
小朋友答錯了，就用實物跟他排一次：13粒豆拿走5粒，親眼看著整個過程。之後口頭重溫步驟：「先減3到10，再減2。」步驟說得多，就會內化成心算。
When your child gets one wrong, lay it out with real objects: 13 beans, take away 5, and watch the process together. Then retell the steps out loud: "first take 3 to reach 10, then take 2." Steps spoken often enough become mental maths.
吃飯情境最實用：「碟子裡有12粒提子，吃了4粒，還有幾粒？」偶然換個問法：「5加多少才是13？」— 加減互逆的感覺，是學好減法的關鍵。
Mealtimes are perfect: "There are 12 grapes on the plate, we ate 4 — how many are left?" Occasionally flip the question: "5 plus what makes 13?" — feeling that addition and subtraction are inverses is the key to mastering subtraction.