Comparing Fraction Products to 1
Comparing Fraction Products to 1 is a Grade 5 math skill from Illustrative Mathematics Chapter 6 (Place Value Patterns and Decimal Operations) that teaches students to determine whether a product of two fractions is greater than, less than, or equal to 1 without calculating. When both fractions are less than 1, their product is always less than 1. When one fraction is greater than 1 and the other is less than 1, the result must be computed to determine the comparison.
Key Concepts
Property To compare the product of two fractions to 1 without calculating, examine each fraction. If both fractions are less than 1, their product will also be less than 1. If one fraction is greater than 1 and the other is less than 1, their product could be greater than, less than, or equal to 1.
Examples Is $\frac{3}{4} \times \frac{7}{8}$ greater than or less than 1? Since $\frac{3}{4} < 1$ and $\frac{7}{8} < 1$, their product is less than 1. Is $\frac{2}{5} \times \frac{4}{3}$ greater than or less than 1? We cannot tell without calculating because $\frac{2}{5} < 1$ and $\frac{4}{3} 1$. In this case, $\frac{2}{5} \times \frac{4}{3} = \frac{8}{15}$, which is less than 1. Is $\frac{5}{2} \times \frac{3}{4}$ greater than or less than 1? We cannot tell without calculating because $\frac{5}{2} 1$ and $\frac{3}{4} < 1$. In this case, $\frac{5}{2} \times \frac{3}{4} = \frac{15}{8}$, which is greater than 1.
Explanation This skill helps you estimate the size of a product involving fractions by comparing it to the benchmark of 1. When you multiply a number by a fraction less than 1, the result is smaller than the original number. Therefore, multiplying two fractions that are both less than 1 will always result in a product that is even smaller and thus less than 1. However, if one factor is greater than 1 and the other is less than 1, you must perform the calculation to determine how the product compares to 1.
Common Questions
How do you compare a product of two fractions to 1 without calculating?
If both fractions are less than 1, their product is always less than 1. If both are greater than 1, the product is greater than 1. If one fraction is greater than 1 and the other is less than 1, you must calculate to determine the comparison.
Why is the product of two fractions less than 1 always less than 1?
Multiplying by a fraction less than 1 shrinks the number. So if you start with a number less than 1 and multiply by another fraction less than 1, the result is even smaller and therefore still less than 1.
What chapter covers comparing fraction products in Illustrative Mathematics Grade 5?
Comparing fraction products to 1 is covered in Chapter 6 of Illustrative Mathematics Grade 5, titled Place Value Patterns and Decimal Operations.
What is an example of comparing a fraction product to 1?
Is (3/4) × (7/8) greater than or less than 1? Since both fractions are less than 1, the product is less than 1. Is (5/2) × (3/4) greater or less than 1? Since one factor is greater than 1 and the other less than 1, you must calculate: (5/2) × (3/4) = 15/8 > 1.
Why is comparing to 1 a useful benchmark in fraction multiplication?
The number 1 is a natural benchmark because it represents a whole. Knowing whether a product is greater than, equal to, or less than 1 helps students estimate and check their work, and builds number sense for fraction operations.