How to calculate 45-27 using the concept of borrowing in subtraction?

Here is the discussion (interactive exchange of opinions) for the teacher's instruction, focusing on Task 2 from the Lesson Flow:

Task 2: Think how to calculate $45-27$ and solve the problem.

The interactive exchange of opinions occurs as the teacher guides students through the concept of borrowing in subtraction:

• The teacher (T) initiates the discussion by asking students to confirm that they cannot subtract 7 from 5 in the ones place. This prompts students to acknowledge the problem and think about solutions.
• Students (S) are then encouraged to think about how to subtract the ones place to find the answer. This is where students might propose different ideas or express confusion, leading to an exchange of thoughts.
• The teacher (T) advises students to manipulate counting blocks to visualize the process. This hands-on activity facilitates discussion as students explain what they are doing with the blocks and why.
• Through this manipulation, students (S) are expected to recognize that a set of 10 blocks (a ten) must be broken into 10 single blocks (ones) when moved to the ones place. This recognition is a key point for discussion, where students articulate their understanding.
• The teacher (T) then assists students in understanding that because 1 ten was borrowed, the tens digit (4) has now become 3. This is another point for clarification and discussion, ensuring students grasp the change in the tens place.

This sequence involves the teacher posing questions, students attempting to solve and explaining their reasoning (often with physical blocks), and the teacher providing guidance and clarification, forming an interactive exchange of opinions and understanding.