The equation you provided, \( 893 + \text{some number} = 506 \), suggests that we need to find the number that, when added to 893, equals 506. To solve for that number, we can rearrange the equation:
\[ \text{some number} = 506 - 893 \]
Calculating the right side:
\[ 506 - 893 = -387 \]
So, the complete equation is:
\[ 893 + (-387) = 506 \]
Therefore, \(-387\) is the number that needs to be added to \(893\) to equal \(506\).