To find the mistake, we can solve the equation step by step. The given equation is:
\[ \frac{x}{2} = -12 \]
To solve for \( x \), you need to eliminate the fraction by multiplying both sides of the equation by 2:
\[ x = -12 \times 2 \]
Calculating that, we have:
\[ x = -24 \]
The mistake in the original statement is the claim that the answer is 24. The correct answer is actually -24.
So, the mistake lies in the misunderstanding of how to isolate \( x \) and in miscalculating the multiplication. The correct solution yields \( x = -24 \).