How do you model - 9 - (-4) with interger chips

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.