Addition and subtraction - Subtract one from two-digit numbers 2 - Presentation

In Lesson 15, students delve into the concept of subtracting one-digit numbers from two-digit numbers, with a particular focus on understanding and utilising multiples of 10 to simplify the subtraction process. The lesson introduces the idea of using a number line to visually aid the subtraction, where students learn to identify the nearest multiple of 10 to the two-digit number and use it as a stepping stone in their calculation. For instance, when subtracting 4 from 23, the students are guided to first subtract 3 to reach the multiple of 10 (which is 20 in this case), and then subtract the remaining 1 to find the final answer. This method is reiterated with various examples to reinforce the concept.

As the lesson progresses, students are encouraged to engage in various activities that challenge them to apply this strategy in different scenarios. They are tasked with finding the difference between numbers using the number line and also through partitioning and exchanging techniques. For example, to subtract 7 from 24, they learn to exchange one 10 for 10 ones to have enough ones to subtract from. The lesson concludes with independent work where students practice the method by finding answers using number lines, partitioning numbers, and drawing diagrams. They are also asked to reflect on the efficiency of the method and to verify the correctness of given statements, fostering a deeper understanding of the subtraction process.