Addition and subtraction - Add and subtract three-digit and ​two-digit numbers not crossing 100 - Presentation

In a mathematics lesson focused on adding and subtracting three-digit and two-digit numbers without crossing the hundred boundary, students are encouraged to apply their understanding of counting in tens. The lesson prompts the question, "What is a multiple of 10?" to engage students in discussion about the concept. Through a series of activities, learners use place value counters to complete number sentences, reinforcing their grasp of how the tens column changes during these operations. For example, when adding five tens to 328, the result is 378, and when subtracting two tens from the same number, it becomes 308. These exercises help students to visually and conceptually understand the process of addition and subtraction with respect to place value.

Further activities involve solving problems like 653 plus three tens and 653 minus three tens, with the outcomes being 683 and 623 respectively. A more complex task asks students to subtract forty from 685, using a step-by-step approach that includes building, drawing, explaining, and then solving a word problem related to the calculation. This multi-faceted approach ensures that children not only perform the calculations but also comprehend the underlying concepts. The lesson concludes with comparison exercises using symbols and reasoning tasks where students must identify and correct mistakes, such as recognizing that subtracting fifty from 368 should result in 318, not 363. These activities are designed to deepen the students' understanding of the relationship between addition, subtraction, and place value.