In this Grade 5 lesson from Illustrative Mathematics Chapter 3, students learn to multiply two non-unit fractions by using area diagrams and written expressions. Students discover that the product of two fractions equals the product of the numerators over the product of the denominators, such as finding that 3/6 × 4/5 = (3×4)/(6×5). This builds toward a generalized understanding of fraction multiplication aligned with standard 5.NF.B.4.b.
Section 1
Interpreting Area Models for Fraction Multiplication
To find the multiplication expression from an area model, identify the two fractions. The first fraction, , is the area shaded in one direction. The second fraction, , is the portion of that already shaded area that is re-shaded or cross-hatched.
Section 2
The Standard Algorithm for Fraction Multiplication
To multiply two fractions, multiply the numerators to find the new numerator and multiply the denominators to find the new denominator.
Expand to review the lesson summary and core properties.
Section 1
Interpreting Area Models for Fraction Multiplication
To find the multiplication expression from an area model, identify the two fractions. The first fraction, , is the area shaded in one direction. The second fraction, , is the portion of that already shaded area that is re-shaded or cross-hatched.
Section 2
The Standard Algorithm for Fraction Multiplication
To multiply two fractions, multiply the numerators to find the new numerator and multiply the denominators to find the new denominator.