Adding and Subtracting Fractions with Like Units
This Grade 4 Eureka Math skill teaches students to add and subtract fractions with the same denominator by operating only on the numerators. The denominator (unit) stays constant because the size of the parts does not change. For example, 3 fifths + 2 fifths = 5 fifths = 5/5, and 7 eighths minus 4 eighths = 3 eighths. This like-units concept, taught in Chapter 24 of Eureka Math Grade 4, mirrors addition and subtraction of any same-unit quantities and forms the basis for all fraction arithmetic.
Key Concepts
To add or subtract fractions with the same denominator (like units), add or subtract the numerators and keep the denominator the same. $$\frac{a}{c} + \frac{b}{c} = \frac{a+b}{c}$$ $$\frac{a}{c} \frac{b}{c} = \frac{a b}{c}$$.
Common Questions
How do you add fractions with the same denominator?
Add only the numerators and keep the denominator the same. For example, 3/5 + 2/5 = (3+2)/5 = 5/5.
How do you subtract fractions with the same denominator?
Subtract the numerators and keep the denominator the same. For example, 7/8 minus 4/8 = (7-4)/8 = 3/8.
Why does the denominator not change when adding or subtracting fractions?
The denominator names the size of each part. Adding or subtracting does not change the size of parts, only how many you have. Just as 3 oranges + 2 oranges = 5 oranges, 3 eighths + 2 eighths = 5 eighths.
What does like units mean in fraction addition?
Like units means the fractions have the same denominator. The denominator names the unit (fourths, fifths, etc.), and you can only add or subtract directly when the units match.
What if the sum of numerators equals the denominator?
The resulting fraction equals 1 whole. For example, 3/5 + 2/5 = 5/5 = 1.