Objective: Use visual models to add and subtract two fractions with the same units, including subtracting from one whole.
In Lesson 17, students decompose a whole into a fraction having the same denominator as the subtrahend. For example, 1 – 4 fifths becomes 5 fifths – 4 fifths = 1 fifth, connecting with Topic B skills. They then see that, when solving 1 2/5 – 4/5 , they have a choice of subtracting 4/5 from 7/5 or from 1. Students model with tape diagrams and number lines to understand and then verify their numerical work.
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