The proportion of potassium nitrate, sulfur, and charcoal in the formulation of ancient Chinese "black powder" is $15: 2: 3$. Given 50 kilograms of charcoal, to prepare "black powder" weighing 1000 kilograms, how many more kilograms of charcoal are needed?
9. Answer: 100

Analysis: Given the ratio of potassium nitrate, sulfur, and charcoal is 15: $2: 3$, the proportion of charcoal is $\frac{3}{20}$. Therefore, to prepare 1000 kilograms of "black powder," the amount of charcoal needed is $1000 \times \frac{3}{20} = 150$ (kilograms). Given that there are already 50 kilograms of charcoal, an additional 150 kilograms - 50 kilograms $=100$ kilograms of charcoal are needed.