Continue writing the next sentence in this paragraph:

How to do grade 9 mathematical processes 
Do operations with fractions. 
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.