分数のたし算・ひき算

When fractions have the same denominator, just add or subtract the numerators and keep the denominator the same. For example, $\frac{2}{7}+\frac{3}{7}=\frac{5}{7}$. Think of it as 2 pieces plus 3 pieces of the same size ($\frac{1}{7}$), making 5 pieces. Subtraction works the same way: $\frac{5}{8}-\frac{1}{8}=\frac{4}{8}$.

When the denominators are different, you cannot add yet — first make them the same. In $\frac{1}{2}+\frac{1}{4}$, change $\frac{1}{2}$ into quarters. Multiply top and bottom by 2: $\frac{1}{2}=\frac{2}{4}$. Now $\frac{2}{4}+\frac{1}{4}=\frac{3}{4}$. When one denominator is a multiple of the other, you only need to change one of the fractions.

Once you have your answer, write it in its simplest form. This is called simplifying. Divide the numerator and denominator by the same number. For example, $\frac{4}{8}$ becomes $\frac{1}{2}$ by dividing top and bottom by 4. And $\frac{6}{8}$ becomes $\frac{3}{4}$ by dividing by 2. When no number divides both any further, you are done.