📚 Student's Edition: Grade 2 Lesson 16-10 – Two-Step Addition and Subtraction Word Problems | 学生版：二年级第16-10课——两步加减法应用题
Welcome to this lesson on two-step addition and subtraction word problems. This topic helps you build the reading and reasoning skills needed for more advanced IGCSE mathematics.
欢迎学习两步加减法应用题。本主题帮助你培养阅读与推理能力，为更高阶的 IGCSE 数学打下基础。
1. Learning Objectives | 学习目标
By the end of this lesson, you should be able to identify a two-step word problem, choose addition or subtraction for each step, write a number sentence, and check your final answer.
学完本课后，你应该能够识别两步应用题，为每一步选择加法或减法，写出算式并检查最终答案。
- Read and understand the problem | 阅读并理解题意
- Find the hidden middle step | 找到隐藏的中间步骤
- Use addition or subtraction correctly | 正确使用加法或减法
- Check using inverse operations | 用逆运算进行检查
2. What Is a Two-Step Word Problem? | 什么是两步应用题
A two-step word problem cannot be solved with one operation only. You must solve a smaller question first, and then use that answer in a second calculation.
两步应用题不能只靠一步运算解出。你必须先解决一个小问题，再用得到的答案进行第二次计算。
Example: Ava has 12 red pencils and 13 blue pencils. She gives 7 pencils to Ben. How many pencils does Ava have left? First add 12 and 13, then subtract 7.
示例：Ava 有 12 支红色铅笔和 13 支蓝色铅笔。她给了 Ben 7 支铅笔。Ava 还剩多少支铅笔？先把 12 和 13 相加，再减去 7。
12 + 13 = 25
25 − 7 = 18
3. Reading and Underlining Key Information | 阅读并圈画关键信息
Before you calculate, read the problem twice. Underline the numbers and circle the question. This stops you from using the wrong numbers or answering the wrong question.
计算之前，请把题目读两遍。划出数字并圈出问题。这可以防止你用错数字或答错问题。
- in total — 一共
- left — 剩下
- more than — 比……多
- fewer than — 比……少
- altogether — 总共
4. Step 1: Use Addition to Combine Parts | 第一步：用加法合并部分
If the problem asks for a total or combines two groups, use addition. The first step is often to find the total number of items before something is taken away.
如果题目要求总数或合并两组，请使用加法。第一步通常是先求出物品总数，再进行后面的拿走或比较。
Example: Liam has 34 marbles. Mia gives him 28 more marbles. Then Liam loses 15 marbles. How many marbles does he have now?
示例：Liam 有 34 颗弹珠。Mia 又给他 28 颗弹珠。然后 Liam 丢了 15 颗弹珠。他现在有多少颗弹珠？
First step: add the marbles to find the total before losing any.
第一步：相加求出丢失前的总数。
34 + 28 = 62
5. Step 2: Use Subtraction to Find the Difference or Remainder | 第二步：用减法求差或剩余
After you have the total, use subtraction if something is taken away, given away, or compared. The answer tells you how many remain or how many more one group has.
得到总数后，如果有物品被拿走、送出或要进行比较，请使用减法。答案告诉你剩余多少或一组比另一组多多少。
Second step: subtract the marbles that were lost.
第二步：减去丢失的弹珠。
62 − 15 = 47
Final answer: Liam has 47 marbles.
最终答案：Liam 有 47 颗弹珠。
6. Using Bar Models to Show the Problem | 用条形模型表示问题
A bar model turns the word problem into a picture. Draw one bar for the total and separate bars for the parts. This helps you see whether you should add or subtract.
条形模型能把应用题变成图形。画一个长条表示总数，再分成表示各部分的小条。这能帮助你判断应该相加还是相减。
- Draw a long bar for the whole | 画一条长条表示整体
- Split it into known and unknown parts | 分成已知部分和未知部分
- Label the numbers and the question mark | 标出数字和问号
7. Writing a Number Sentence | 写出算式
Write the number sentence in the order you solve it. You can use brackets to show the first step clearly. For example, (23 + 19) − 11 means add 23 and 19 first, then subtract 11.
按解题顺序写算式。可以使用括号清楚表示第一步。例如 (23 + 19) − 11 表示先把 23 和 19 相加，再减去 11。
(23 + 19
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