Answer
$-10\lt-5$
Work Step by Step
We know that $-5\gt-10$, because -5 is to the right of -10 on the number line.
That being said, we can also say that $-10\lt-5$, because -10 is to the left of -5 on the number line (which means that -10 has a value that is less than that of -5).
