1. **State the problem:** It takes 48 minutes for 7 people to paint 7 walls. We want to find how many minutes it takes 20 people to paint 20 walls. 2. **Understand the relationship:** The work done (painting walls) depends on the number of people and the time they work. If more people work, the time taken decreases proportionally, assuming all work at the same rate. 3. **Calculate the rate per person:** Since 7 people paint 7 walls in 48 minutes, 1 person paints 1 wall in 48 minutes (because the work is evenly distributed). 4. **Apply to 20 people and 20 walls:** Since 1 person paints 1 wall in 48 minutes, 20 people painting 20 walls will also take 48 minutes because the ratio of people to walls remains the same. **Final answer:** $$48$$ minutes