Why Do We Need a Common Denominator When Add/Subtracting Fractions? This video provides a justification for why we need a common denominator when adding or subtracting fractions. https://mathispower4u.com #why, #common, #denominator, #fractions, #add, #addition, #subtract, #subtraction, #arithmetic, #james, #sousa, #review, #math, #mathskills | Mathispower4u