Distance on a number line is the absolute value of the difference: |a − b|. Order does not matter. Absolute value as a set is in absolute value.
Subtract, then drop the sign
From −3 to 5 is 8. From 5 to −3 is also 8. Midpoint on a line is the average, in the midpoint formula.
The short list is in ACT Math formulas.
The bottom line
|a − b|. Distance is never negative.
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