What do you do to the numerator when finding a common denominator for adding or subtracting fractions?

When finding a common denominator for adding or subtracting fractions, the correct approach involves adjusting the numerator to ensure that it corresponds with the new common denominator. By multiplying the numerator by the same factor as the denominator, you maintain the equivalent value of the fraction. This is crucial because fractions represent a ratio, and changing both the numerator and denominator by the same factor does not alter the fraction's value.

For example, if you have the fractions 1/4 and 1/2 and want to add them, you can find a common denominator such as 4. The fraction 1/2 can be converted to have this common denominator by multiplying both the numerator and denominator by 2, resulting in 2/4. This adjustment allows the fractions to be properly combined while still representing the same values.

In summary, adjusting the numerator by multiplying it by the same factor as the denominator ensures that both fractions are expressed in equivalent forms, allowing for accurate addition or subtraction.