心算加法和减法（9岁以上）
Mental addition and subtraction (age 9+)
利用位值知识和已知事实，对越来越大的数进行心算加减。
Add and subtract numbers mentally with increasingly large numbers, using place-value knowledge and derived facts
学习证据 / Evidence
- 心算45,000 + 8,000
- 用往上数的方法心算10,000 − 3,200
- 利用接近加倍的策略：2,500 + 2,600 = 5,100
- Mentally calculate 45,000 + 8,000
- Mentally subtract 3,200 from 10,000 by counting up
- Use near-doubles: 2,500 + 2,600 = 5,100
评估问题 / Assessment
{{name}}能利用位值知识，不用写出来就心算出像“4,700 − 1,300”这样的题目吗？
Can {{name}} work out something like '4,700 − 1,300' in their head using what they know about place value — without needing to write it all out?