To add or subtract mixed numbers, the easiest way is to convert them to improper fractions, or fractions with a larger numerator. Find the least common multiple, and add them like normal fractions.
- Convert all mixed numbers to fractions
To do this, multiply the denominator by the whole number, then add the numerator. This yields the new numerator. Use the original denominator. For example, if you have the mixed number 1 7/8, it is rewritten as 15/8.
- Rewrite all fractions to use the same denominator
With the fraction 15/8, also assume you're subtracting 2 3/4 from this number. Converting it yields 11/4. Eight is the least common multiple of 4 and 8, so you only have to multiply the fraction by 2. This yields 22/8. The denominator does not matter if it's the same.
- Subtract the numerators
The original numerator is 15/8, and subtracting 22/8 yields -7/8. If the result were an improper fraction, you could convert it back to a mixed number by dividing the numerator by the denominator and expressing the remainder as the numerator of the fraction. When you've performed the multiplication, It's best to simplify the fraction, if possible, to make the mixed number easier to read.