Cross-multiply: the larger product points to the larger fraction.
To compare 5/8 and 7/12, multiply across: 5 × 12 = 60 and 7 × 8 = 56. Since 60 > 56, 5/8 is bigger. This shortcut works because it quietly converts both fractions to the same denominator (8 × 12) and just compares the numerators.
