Explanation:
Start with 9 negative chips, for a value of -9.
Take away (subtract) 4 of the negative chips. This is modeling - (-4).
You will be left with 5 negative chips.
-9 - (-4) = -5
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Each negative chip in this scenario models -1. The actions you're doing with the chips are full equivalent to the actions you would do for the subtraction problem 9 - 4 = 5, except that the numbers (chips) are negative, not positive.
