To add or subtract fractions, you generally need

• A. Need a common numerator
• B. Find a common denominator
• C. Convert to decimals first
• D. Need a common denominator

Answer: (D)

To add or subtract fractions, you must have the same size pieces. The denominator tells how many equal parts make up a whole, so if the denominators are different, the parts aren’t the same size and you can’t combine the numerators directly. The fix is to use a common denominator, a shared bottom number, so both fractions are expressed in terms of the same-sized parts. You find a common denominator by taking a common multiple of the original denominators and rewrite each fraction as an equivalent fraction with that denominator. Once they share the same denominator, you simply add or subtract the numerators and keep that denominator, then simplify if possible. Converting to decimals isn’t needed and can introduce rounding errors.