Explain why a fraction a / b is equivalent to a fraction (n × a) / (n × b) by using visual fraction models with attention to how the number and size of the parts differ even though the two fractions themselves are the same size. (nationalmathfoundation.org)
Solve word problems involving addition and subtraction of fractions referring to the same whole including cases of unlike denominators e.g. by using visual fraction models or equations to represent the problem. (nationalmathfoundation.org)
NF.2 — using visual fraction models to add two fractions... (achievethecore.org)