Addition and subtraction - Subtract a three-digit number from a three-digit number exchange - Presentation

The lesson on subtracting a three-digit number from another three-digit number with exchanges delves into the intricacies of borrowing in subtraction. Students are challenged to understand when and why an exchange is necessary during the subtraction process. The lesson begins with a discussion prompt, asking students to ponder on the concept of 'exchange' in the context of subtraction. Visual aids, such as counters, are employed to facilitate a deeper understanding of the concept. For example, when subtracting 224 from 118, students use counters to represent hundreds, tens, and ones, allowing them to visually grasp the exchange process when certain columns lack sufficient value to perform the subtraction.

Further activities involve more complex examples, such as subtracting 638 from 254, where students are encouraged to use counters to represent each place value and execute the necessary exchanges across hundreds, tens, and ones. The lesson progresses to column subtraction exercises, demonstrating exchanges through written methods. For instance, subtracting 135 from 252 requires an exchange from the tens to the ones column. The lesson also incorporates reasoning tasks where students identify missing digits in subtraction equations and correct mistakes in given calculations, such as Esin's error in subtracting 389 from 506. These activities help students to not only perform subtraction with exchanges but also understand the logic behind the process and how to articulate this knowledge to others.