Use addition to rewrite the subtraction expression -20 - (-6) without changing the digits. Do not solve.

Step-by-step solution

1. 1

   State the rule being tested. Subtraction is defined as adding the opposite:

   $a-b=a+(-b).$

   The instruction to keep the digits unchanged means only signs may move — $20$ stays $20$ and $6$ stays $6$.

2. 2

   Identify a and b in the expression. Here $a=-20$ and $b=-6$. The first minus is a sign attached to $20$; the second minus is the operation; the third is the sign attached to $6$.

3. 3

   Replace the operation and take the opposite of b. The operation becomes addition, and $b=-6$ has opposite $-(-6)=+6$:

   $-20-(-6)=-20+6.$

   Only the middle two signs changed — this is the 'keep, change, change' pattern: keep the first number, change the operation, change the sign of the second.

4. 4

   Watch what did not change. The leading $-20$ keeps its own negative sign. A frequent mistake is to flip that one too and write $20+6$, which is a different number entirely.

5. 5

   Confirm the two forms agree. The task says not to solve, but as a private check: $-20-(-6)$ means starting at $-20$ and removing a debt of $6$, which lands on $-14$; and $-20+6=-14$ as well. The rewritten expression is $-20+6$.