Question

Elaine used the subtraction algorithm to subtract −17−(−3). She got the answer −14, but she does not feel confident that she is correct. Connect the expression −17−(−3) to a two-color counter model. Explain how the two-color counter model can be used to confirm whether Elaine’s answer is correct.

Answer 1

In a two-color counter model, each counter can represent a positive or negative value. The two colors typically used are red for negative values and yellow for positive values.

To model the expression −17−(−3), we start with 17 red counters to represent -17. Then, we remove 3 red counters to represent -(−3).

If Elaine's answer of -14 is correct, the final result should be 14 red counters (representing -14) on the table.

By physically representing the expression using two-color counters, Elaine can count the number of red counters left on the table. If there are indeed 14 red counters remaining, it confirms that her answer of -14 is correct. However, if she counts a different number, she can re-evaluate her subtraction algorithm or double-check her calculations to find any mistakes.