Answer
$-6.8$
Work Step by Step
In adding two numbers with the same sign, perform the following steps:
(1) Add their absolute values.
$|-1.5| + |-5.3| = 1.5 + 5.3 = 6.8$
(2) The sum must have sign common to the addends.
$-1.5+(-5.3) = -6.8$
Thus, the sum is $-6.8$.