Math Problem Solver

\[ \frac{5}{7} - \frac{3}{21} = \frac{4}{7} = 0.\overline{571428} \]

The sum can be computed by rewriting each term over a common denominator, where the least common denominator of \(\frac{5}{7}\) and \(\frac{-3}{21}\) is \(21\). \[ \begin{aligned} \frac{5}{7} - \frac{3}{21} &= \frac{5 \cdot 3}{7 \cdot 3} + \frac{-3 \cdot 1}{21 \cdot 1} \\ &= \frac{15 + -3}{21} \\ &= \frac{12}{21} \\&= \frac{4}{7} \end{aligned} \]