Addition and subtraction - Subtract a two-digit number from a ​three-digit number crossing 10 or 100​ - Presentation

The presentation provides a comprehensive guide for teaching Year 3 students how to subtract a two-digit number from a three-digit number, particularly when the subtraction involves crossing tens or hundreds. The lesson begins with a discussion on the use of part-whole models in subtraction, encouraging students to think about whether they are finding the whole or the part in the process. The first activity challenges students to represent the subtraction of two-digit numbers from three-digit numbers using base 10 blocks, prompting them to consider what to do when there are insufficient ones to subtract, and how to make exchanges from the tens or hundreds.

Further activities involve more complex scenarios, such as exchanging ten tens for a hundred when performing column subtraction, and using comparison symbols to evaluate the results of different subtraction problems. Students are encouraged to think critically about the efficiency of various methods for solving subtraction problems, with examples provided for discussion and reasoning. Independent work tasks reinforce the concepts taught, offering opportunities for students to practice column subtraction and to consider alternative ways of representing calculations. Throughout the lesson, students are guided to understand the importance of exchanging and regrouping in subtraction, ensuring they grasp the key concepts necessary for mastering subtraction across tens and hundreds.