How would you wright this as a decimal number ?

Hi there! :)
[tex]\large\boxed{-8.4}[/tex]
We can calculate the decimal by converting the fraction to an improper fraction, then dividing.
Derive the inpromper fraction by:
[tex]a\frac{b}{c} = \frac{c * a + b}{c}[/tex]
In this instance:
[tex]-8\frac{2}{5} = \frac{-8* 5 -2 }{5} = \frac{-42}{5}[/tex]
Divide:
-42 ÷ 5 = -8.4.