The Key is Still the Denominator
Just like with adding fractions, the first step to subtracting them is to check to see if the denominators are the same. If they are the same, then great! Move the denominator over as part of your answer, then subtract the two numerators.
When Denominators Are Not the Same
Again, treat the problem as you would when adding fractions with unlike denominators. You must find the lowest common denominator, LCD. Remember the LCD is the lowest number that both denominators in the problem can divide into equally. Let’s revisit the same problem from the addition page:
Did you notice that your new numerator and denominator can be reduced to the original fractions in the problem? That makes a good self-check if you are in doubt that your math is correct.