[header] How to do grade 9 mathematical processes [title] Do operations with fractions. [substeps] Add and subtract. Fractions can only be added, or subtracted, if they have the same denominator, otherwise the answer is incorrect. 
For example , 2/5 + 1/5 = 3/5. To add or subtract fractions with different denominators, the first step is to find the lowest common denominator.