Nadie has a chip board with 4 red chips. She needs to subtract 2 black chips, but there are no black chips on the board. Nadie says, "it is impossible to subtract 2 black chips. There are none on the board "What can Nadine do to the chip board so that she can subtract 2 black chips? Explain your reasoning.
Nadie can have a black that is attacked with a red twice, there together, so they cancel each other. Then you can break them apart. After that you can now subtract the two black chips which leaves you with 6 red chips.(-6)
without some way to change her red chips to black ones, it's hard to say.
Or, she can write an IOU -- in effect, borrow some black chips till the final reckoning is done.
I think she can change 2 of her red pieces to black pieces so know she has 2 black pieces and 2 red pieces and that way she can take her 2 black pieces and still have 2 red pieces on the board and she can make it into a number sentences.
To enable Nadie to subtract 2 black chips from the chip board, she can add 2 black chips to the board.
By doing so, the board will have a total of 4 red chips and 2 black chips. Now, Nadie can subtract the 2 black chips as desired.
Essentially, Nadie's statement that it is impossible to subtract 2 black chips is correct because initially, there were no black chips on the board. However, by adding black chips to the board, Nadie creates the necessary conditions to subtract them.