逆运算：加法和减法互为逆运算
Inverse: addition undoes subtraction
认识并运用加法和减法之间的逆运算关系来检验计算结果，并解决求未知数的问题。
Recognise and use the inverse relationship between addition and subtraction to check calculations and solve missing-number problems
学习证据 / Evidence
- 用 22 − 7 = 15 来检验 15 + 7 = 22。
- 利用逆运算求解：□ + 9 = 14，所以 □ = 14 − 9 = 5。
- 解释加法和减法互相“抵消”，也就是互为逆运算。
- Check 15 + 7 = 22 by calculating 22 − 7 = 15
- Use the inverse to solve: □ + 9 = 14, so □ = 14 − 9 = 5
- Explain that addition and subtraction 'undo' each other
评估问题 / Assessment
如果{{name}}算出 13 + 5 = 18，他们能马上利用这个结果说出“18 − 5 = 13”吗，而不用重新算一遍减法？
If {{name}} works out 13 + 5 = 18, can they immediately use that to say '18 − 5 = 13' — without having to work the subtraction out all over again?