1. **State the problem:** We have two trains moving in the same direction with speeds 11 km/hr and 12 km/hr. We need to find their relative speed. 2. **Formula and concept:** When two objects move in the same direction, the relative speed is the difference of their speeds. $$\text{Relative speed} = |v_2 - v_1|$$ where $v_1$ and $v_2$ are the speeds of the two trains. 3. **Apply the formula:** $$\text{Relative speed} = |12 - 11| = 1 \text{ km/hr}$$ 4. **Explanation:** The relative speed tells us how fast one train is moving compared to the other. Since they move in the same direction, we subtract the smaller speed from the larger speed. **Final answer:** The relative speed of the two trains is $1$ km/hr.