Rational number $\dfrac{p}{q}$ is in standard form, if:

1. p and q have no common factor and p ≠ 0
2. p and q have at least one common factor other than 1 and q ≠ 0
3. p and q have no common factor and q ≠ 0
4. p is divisible by q completely.

The addition of two rational number $\dfrac{a}{b}$ and $\dfrac{c}{d}$ is commutative, if

1. $\dfrac{a}{b} + \dfrac{c}{d}$ is rational number

2. $\dfrac{a+c}{b +d}$ is a rational number.

3. $\dfrac{a}{b} + \dfrac{c}{d}$ = $\dfrac{c}{d} + \dfrac{a}{b}$

4. $\dfrac{a}{b} - \dfrac{c}{d}$ = $\dfrac{c}{d} - \dfrac{a}{b}$

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

$\dfrac{-5}{8}$ and $\dfrac{3}{8}$

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

$\dfrac{-8}{13}$ and $\dfrac{-4}{13}$