When adding fractions, the denominators must be the same.

• A. The numerators must be equal
• B. The denominators must be the same
• C. The fractions must be in lowest terms
• D. The fractions must be multiplied

Answer: (B)

When adding fractions, you must express them with a common denominator so you’re adding parts of the same size. Having the same denominator provides a common unit to measure the parts, allowing you to combine the numerators directly. For example, 1/3 + 1/4 isn’t easily added because a third and a quarter aren’t the same size; convert them to a common denominator like 12, giving 4/12 + 3/12, which equals 7/12. After you’ve rewritten them with a common denominator, you add the numerators and keep that denominator. The numerators don’t need to be equal, and the fractions don’t have to be in lowest terms before adding—simplification is a separate step after you perform the addition. Multiplication is not involved in this operation.