# How do you evaluate -\frac { 9} { 10} + ( - \frac { 4} { 5} )?

Feb 8, 2017

$- \frac{9}{10} + \left(- \frac{4}{5}\right) = - \frac{17}{10}$

#### Explanation:

First, find a common denominator. Since, $2 \times 5 = 10$ then,

$\frac{4}{5} \times 1 = \frac{4}{5} \times \frac{2}{2} = \frac{4 \times 2}{5 \times 2} = \frac{8}{10}$

Then

$- \frac{9}{10} + \left(- \frac{4}{5}\right) = - \frac{9}{10} + \left(- \frac{8}{10}\right)$

Since both fractions are negative we can factor out $- 1$

Then

$- \frac{9}{10} + \left(- \frac{8}{10}\right) = - 1 \times \frac{9 + 8}{10} = - 1 \times \frac{17}{10} = \underline{- \frac{17}{10}}$

Feb 8, 2017

$- 1 \frac{7}{10}$

#### Explanation:

$- \frac{9}{10} + \left(- \frac{4}{5}\right)$

$\therefore = - \frac{9}{10} - \frac{4}{5}$

$\therefore = \frac{\left(1 \times - 9\right) - \left(2 \times 4\right)}{10}$

$\therefore = \frac{- 9 - 8}{10}$

$\therefore = - \frac{17}{10}$

$\therefore = - 1 \frac{7}{10}$