Two-Color Counters

I've only used Two-Color Counters to add and subtract integers.

Red = Negative
Yellow = Positive
Red + Yellow = "Zero Pair" = 0 (zero)

ADDITION

(-3) + (-2) = -5

3 Red + 2 Red = 5 Red

(+4) + (+1) = +5

4 Yellow + 1 Yellow = 5 Yellow

(+4) + (-2) = +2

4 Yellow + 2 Red (Remove 2 Zero Pairs) = 2 Yellow

(-5) + (+3) = -2

5 Red + 3 Yellow (Remove 3 Zero Pairs) = 2 Red

SUBTRACTION

(-5) - (-2) = -3

Start with 5 Red, then remove 2 Red = 3 Red

(+3) - (+2) = +1

Start with 3 Yellow, then remove 2 Yellow = 1 Yellow

(-8) - (+3) = -11

Start with 8 Red. You can't subtract 3 Yellow because you don't have any, so you have to add 3 Zero Pairs. Now you can take away the 3 Yellow = 11 Red

(+6) - (-2) = +8

Start with 6 Yellow. You can't subtract 2 Red because you don't have any, so you have to add 2 Zero Pairs. Now you can take away the 2 Red = 8 Yellow