Grade 6 Math: Subtracting Fractions with Unlike Denominators

Grade 6 focus: Subtracting fractions with unlike denominators uses the same rewriting process as addition: find a common denominator (preferably the LCD), rewrite each fraction, then subtract the numerators.

Video lesson: Watch this Khan Academy tutorial for a clear walk-through.

Method

1. Find the LCD of the denominators.
2. Rewrite each fraction as an equivalent fraction with that denominator.
3. Subtract the numerators; keep the denominator.
4. Simplify the result if needed.

Worked example

Compute \(\frac{7}{10} – \frac{1}{4}\).

\(\mathrm{LCM}(10,4)=20\). Then \(\frac{7}{10} = \frac{14}{20}\) and \(\frac{1}{4} = \frac{5}{20}\). Difference: \(\frac{14}{20} – \frac{5}{20} = \frac{9}{20}\).

Borrowing from the whole

When the first numerator is too small (in mixed-number form), you may need to regroup—borrow \(1\) whole from the integer part and rewrite it as a fraction with the same denominator. That skill pairs directly with this lesson.

Common mistakes

• Subtracting numerators before making denominators match.
• Using an incorrect equivalent fraction when scaling.
• Leaving a negative intermediate step unaddressed when working with mixed numbers.

Fluency check

Try \(\frac{5}{6} – \frac{3}{8}\). LCD \(= 24\): \(\frac{20}{24} – \frac{9}{24} = \frac{11}{24}\).