Answer
$-1.3$
Work Step by Step
In adding two numbers with the same sign, perform the following steps:
(1) Add their absolute values.
$|-0.4| + |-0.9| = 0.4 + 0.9 = 1.3$
(2) The sum must have sign common to the addends.
$-0.4+(-0.9) = -1.3$
Thus, the sum is $-1.3$.
