四舍五入估算
Estimating by rounding
估算计算结果，并利用逆运算来检验答案；在数字越来越大时，运用四舍五入和逆向推理进行估算与验算。
Estimate the answer to a calculation and use inverse operations to check answers; apply to increasingly large numbers using rounding and inverse reasoning
学习证据 / Evidence
- 计算前先把数字四舍五入到最接近的十位或百位，估算出和或差。
- 用加法检验减法答案，反之亦然。
- 能根据估算结果判断计算出的答案是否不合理。
- 计算前先把数字四舍五入，估算出和或差。
- 用加法验算减法答案，用减法验算加法答案。
- 能通过和估算结果比较，发现计算出的答案不合理。
- Round numbers to the nearest 10 or 100 to estimate a sum or difference before calculating
- Use addition to check a subtraction answer, or vice versa
- Identify when a calculated answer is unreasonable based on the estimate
- Round numbers to estimate a sum or difference before calculating
- Use addition to check a subtraction answer and vice versa
- Identify an unreasonable answer by comparing to the estimate
评估问题 / Assessment
在{{name}}开始计算之前，能否先做出合理的粗略估算，然后用逆运算来检验答案？
Before {{name}} works out a calculation, can they make a sensible rough guess — and then check their answer using the opposite operation?