Question

The sum of two rational numbers is $\frac{4}{21}$. If one of them is $\frac{5}{7}$, find the other.

Answer 1

$\begin{array}{l}\\ \text{Let the other number that be}\mathit{\text{x.}}\\ \\ \frac{5}{7}+x=\frac{4}{21}\\ =>x=\frac{4}{21}-\frac{5}{7}\\ \mathrm{L}.\mathrm{C}.\mathrm{M}.\mathrm{of}21\mathrm{and}7\mathrm{is}21.\\ \begin{array}{l}=>x=\frac{4-15}{21}\\ =>x=\frac{-11}{21}\end{array}\\ \text{Hence, the required number is}\frac{-11}{21}\text{.}\end{array}$