a Understand addition and subtraction of fractions as joining and separating parts referring to the same whole.
b Decompose a fraction into a sum of fractions with the same denominator in more than one way, recording each decomposition by an equation. Justify decompositions, e.g., by using a visual fraction model. Examples: $\frac38 = \frac18 + \frac18 + \frac18$; $\frac38 = \frac18 + \frac28$; $2 \frac18 = 1 + 1 + \frac18 = \frac88 + \frac88 + \frac18.$
c Add and subtract mixed numbers with like denominators, e.g., by replacing each mixed number with an equivalent fraction, and/or by using properties of operations and the relationship between addition and subtraction.
d Solve word problems involving addition and subtraction of fractions referring to the same whole and having like denominators, e.g., by using visual fraction models and equations to represent the problem.