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the movement is 0–2=–2. b. From 0 to –3, the movement is –3–0=–3. The total
movement is the sum of the two movements: – 3 + (– 2) = – 5.

 Converting subtraction to addition and addition to subtraction

Recall that Target Floor – Starting Floor = Movement needed
or
Target Floor = Starting Floor + Movement needed

If we start at 2 and wish to go to –3, what is the movement needed?
First method: Looking at the number line, we see we need to move –5
(i.e., 5 in the backward direction). Therefore, – 3 – 2 = – 5. The movement
needed is –5.
Second method: Break the journey from 2 to –3 into two parts. a. From 2
to 0, the movement is 0–2=–2. b. From 0 to –3, the movement is –3–0=–3. The
total movement is the sum of the two movements: – 3 + (– 2) = – 5. Look at the
two-coloured expressions. There is no subtraction in the second one! In this
way, we can always convert subtraction to addition. The number that is being
subtracted can be replaced by its inverse and then added instead. Similarly, a
number that is being added can be replaced by its inverse and then subtracted.
In this way, we can also always convert addition to subtraction.

Examples:
a. (+7) –(+5) = (+7)+(–5) b. (–3) – (+8) = (–3)+(–8) )

c. (+8) –(–2) = (+8)+(+2) ) d. (+6) – (–9) = (+6)+(+9)