$- \dfrac { 3 } { \color{#FF6800}{ 5 } } - \dfrac { 3 } { \color{#FF6800}{ 4 } }$
$ $ The smallest common multiple in denominator is $ 20$
$- \dfrac { 3 } { \color{#FF6800}{ 5 } } - \dfrac { 3 } { \color{#FF6800}{ 4 } }$
$- \dfrac { 3 } { 5 } - \dfrac { 3 } { 4 }$
$ $ Multiply the denominator and the numerator so that the denominator is the smallest common multiple $ $
$- \dfrac { 3 \times \color{#FF6800}{ 4 } } { 5 \times \color{#FF6800}{ 4 } } - \dfrac { 3 \times \color{#FF6800}{ 5 } } { 4 \times \color{#FF6800}{ 5 } }$
$\color{#FF6800}{ - } \color{#FF6800}{ \dfrac { \color{#FF6800}{ 3 } \color{#FF6800}{ \times } \color{#FF6800}{ 4 } } { \color{#FF6800}{ 5 } \color{#FF6800}{ \times } \color{#FF6800}{ 4 } } } \color{#FF6800}{ - } \color{#FF6800}{ \dfrac { \color{#FF6800}{ 3 } \color{#FF6800}{ \times } \color{#FF6800}{ 5 } } { \color{#FF6800}{ 4 } \color{#FF6800}{ \times } \color{#FF6800}{ 5 } } }$
$ $ Organize the expression $ $
$\color{#FF6800}{ - } \color{#FF6800}{ \dfrac { \color{#FF6800}{ 12 } } { \color{#FF6800}{ 20 } } } \color{#FF6800}{ - } \color{#FF6800}{ \dfrac { \color{#FF6800}{ 15 } } { \color{#FF6800}{ 20 } } }$
$\color{#FF6800}{ - } \color{#FF6800}{ \dfrac { \color{#FF6800}{ 12 } } { \color{#FF6800}{ 20 } } } \color{#FF6800}{ - } \color{#FF6800}{ \dfrac { \color{#FF6800}{ 15 } } { \color{#FF6800}{ 20 } } }$
$ $ Since the denominator is the same as $ 20 $ , combine the fractions into one $ $
$\color{#FF6800}{ \dfrac { \color{#FF6800}{ - } \color{#FF6800}{ 12 } \color{#FF6800}{ - } \color{#FF6800}{ 15 } } { \color{#FF6800}{ 20 } } }$
$\dfrac { \color{#FF6800}{ - } \color{#FF6800}{ 12 } \color{#FF6800}{ - } \color{#FF6800}{ 15 } } { 20 }$
$ $ Find the sum of the negative numbers $ $
$\dfrac { \color{#FF6800}{ - } \color{#FF6800}{ 27 } } { 20 }$
$\dfrac { \color{#FF6800}{ - } \color{#FF6800}{ 27 } } { 20 }$
$ $ Move the minus sign to the front of the fraction $ $
$\color{#FF6800}{ - } \color{#FF6800}{ \dfrac { \color{#FF6800}{ 27 } } { \color{#FF6800}{ 20 } } }$