Fractions - Add and Subtract Fractions (1) - Presentation

In a comprehensive lesson on adding and subtracting fractions, students are introduced to the concept of finding a common denominator by identifying the lowest common multiple (LCM) of the denominators involved. The lesson starts with a discussion on how to find the LCM of two numbers, which is crucial when the denominators are multiples of the same number but not identical. For instance, Esin is faced with the task of adding 5/8 and 3/16, where she determines that the LCM of 8 and 16 is 16. This allows her to convert 5/8 into an equivalent fraction with a denominator of 16, making the addition of the two fractions straightforward. Students are then encouraged to apply this method to various examples, such as adding 1/3 and 2/9 or 3/7 and 7/21, ensuring they understand how to adjust fractions to have a common denominator before performing the operation.

Further activities challenge students to use the LCM to find common denominators for pairs of fractions and then add or subtract them accordingly. For example, they might subtract 5/8 from 3/4 by first converting both fractions to have the same denominator. Real-life applications, such as calculating the amount of paint left after Leanna uses certain fractions over the weekend, help students visualize and understand the practical use of fractions. The lesson also includes reasoning tasks where students must complete calculations with missing digits or identify errors in fraction addition, such as incorrectly adding numerators and denominators without finding a common denominator. These activities are designed to deepen students' understanding and encourage critical thinking about the processes involved in fraction arithmetic.