How it works
These adding and subtracting unlike fractions worksheets come in three levels of common denominator. The page opens on the middle one, denominators with no common factor. Pick another in Sheet type, then press Print. Make a new sheet changes the numbers.
Read the full guide
Three levels of common denominator
Sheet type labels the three levels Easiest, Harder and Hardest. Three fractions, blanks and improper comes after them. When one denominator is a multiple of the other, as in 1/2 + 3/8, only one fraction changes. When the two share no factor, the common denominator is their product: 1/4 + 2/3 = 3/12 + 8/12 = 11/12. When they share a factor but neither divides the other, as with sixths and eighths, the product 48 works. The least common denominator, 24, keeps the numbers smaller.
Where it sits in the standards
Common Core puts unlike denominators in grade 5. Standard 5.NF.1 gives the example 2/3 + 5/4 = 8/12 + 15/12 = 23/12. A grade 4 footnote says they are not required that year. Texas pairs models in 5.3(H) with fluency in 5.3(K).
- Print Rename one fraction, sums past 1 before the harder levels, so turning 11/8 into 1 3/8 is already routine.
- A pupil who always multiplies the denominators needs the least common denominator sheets: 5/6 + 3/8 over 24, not 48.
- Take two fractions from 1 is the pattern behind every problem that asks what fraction is left.
Questions and answers
How do you add fractions with unlike denominators?
Rename both fractions over a common denominator, then add the numerators and keep the denominator: 1/4 + 2/3 = 3/12 + 8/12 = 11/12. Subtracting follows the same steps. The key prints these lines for every problem, so a pupil can find the step that went wrong.
Do you have to use the least common denominator?
No. Any common denominator gives the same sum. For 1/6 + 3/4, the product 24 gives 22/24 and the least common denominator 12 gives 11/12, the same value. Common Core 5.NF.1 states its rule with the product. The least one keeps the numbers smaller.
What grade adds and subtracts fractions with unlike denominators?
Grade 5, in both Common Core and the Texas standards. Grade 4 pupils add and subtract with like denominators, plus tenths and hundredths, which have a page of their own: adding tenths and hundredths.
When is the answer already in lowest terms?
When the two denominators share no factor and both fractions start in lowest terms, the result cannot be simplified: 3/4 − 2/5 = 15/20 − 8/20 = 7/20. So the no common factor sheets practice renaming alone, and simplifying waits for the other two levels.