Add each pair of rational numbers, given below, and show that their addition (sum) is also a rational number:

$\dfrac{7}{-18}$ and $\dfrac{8}{27}$

$\dfrac{7}{-18} + \dfrac{8}{27} \\[1em] \dfrac{-7}{18} + \dfrac{8}{27} \\[1em]$

LCM of 18 and 27 is 2 x 3 x 3 x 3 = 54

$\dfrac{-7 \times 3}{18 \times 3} + \dfrac{8 \times 2}{27 \times 2} \\[1em] =\dfrac{-21}{54} + \dfrac{16}{54} \\[1em] =\dfrac{-21+16}{54} \\[1em] =\dfrac{-5}{54}$

As $\dfrac{-5}{54}$ is in the form of $\dfrac{p}{q}$ where p and q both are integers and q ≠ 0,

∴ $\dfrac{-5}{54}$ is a rational number.