4.NF.A.2
Compare two fractions with different numerators and different denominators, e.g., by creating common denominators or numerators, or by comparing to a benchmark fraction such as 1/2. Recognize that comparisons are valid only when the two fractions refer to the same whole. Record the results of comparisons with symbols >, =, or <, and justify the conclusions, e.g., by using a visual fraction model.
Compare fractions with different numerators and denominators. We use a/b = (n * a)/(n * b) to rewrite each fraction, so they have the same numerator, denominator, or both. Then we compare. This builds on 3.NF.A.3.