How to do add or subtraction fractions?

A fraction a/b consists of a numerator (the part above the bar, a in this example) and a denominator (the part below the bar, b here). In order to add or subtract fractions, we need to make sure the denominators of all terms are the same, and add or subtract the numerators but keeping the denominators unchanged. 

For example, 2/7 + 1/7 = (2+1)/7 = 3/7. 2/7 - 1/7 = (2-1)/7 = 1/7. This is a simple example because the denominators of all terms are alreday the same. However when they are different, we need to use Least Common Muliple (LCM) to covert the fractions into ones with the same denominators, namely LCM. Then do the addtion or subtraction. Let me explain to you with an example. Solve 1/9 + 5/12. Firstly, find LCM of 9 and 12. 9 = 3 x 3. 12 = 2 x 2 x 3. So LCM(9,12) = 2 x 2 x 3 x 3 = 36. Now we need to covert both fractions into ones with denominators 36. essentially coverting1/9 = ?/36. 1/9 = (1x4)/(9x4) = 4/36. 5/12 = (5x3)/(12x3) = 15/36. So 1/9 + 5/12 = 4/36 + 15/36 = 19/36. Done!