Addition, Subtraction, Multiplication and Division - Reason from known facts - Presentation

In a comprehensive lesson focused on the four operations of arithmetic—addition, subtraction, multiplication, and division—students are encouraged to reason from known facts. This approach allows them to solve calculations more efficiently by not having to start from the beginning each time. The lesson delves into important mathematical concepts such as commutativity, which refers to the idea that numbers can be added or multiplied in any order without changing the result, and the inverse, which is the opposite operation that reverses the effect of the original operation (e.g., addition and subtraction are inverses, as are multiplication and division).

Through a series of engaging activities, students apply these concepts to find missing numbers in a set of calculations, such as using the known fact that 90 divided by 2 equals 45 to solve similar problems. They also explore how division facts can assist in answering multiplication questions and vice versa. For example, knowing that 5,138 divided by 14 equals 367 helps students to calculate 15 times 367. The lesson includes reasoning exercises where students determine the truth of given statements based on their calculations and identify which calculations yield the same product as the multiplication of 24 by 5. Independent work prompts students to use commutativity to complete calculations and to prove the accuracy of their answers, reinforcing their understanding of how to reason from known facts in mathematics.