A man walks with speed 15 km/hr instead of 12 km/hr and covers 20 km more distance. Find the distance covered by him with speed 15 km/hr.

Sure, let's solve this step by step:

1. First, let's find out the time he would have taken if he was walking at a speed of 12 km/hr. We know that time = distance/speed. But we don't know the original distance he was supposed to cover. Let's assume that distance to be 'd' km. So, the time taken would be d/12 hours.

2. Now, the man walks 20 km more than the original distance 'd' at a speed of 15 km/hr. So, the time taken for this would be (d+20)/15 hours.

3. According to the problem, these two times are equal because he is spending the same amount of time walking, just at different speeds. So, we can set up the equation d/12 = (d+20)/15.

4. To solve for 'd', we can cross-multiply to get 15d = 12d + 240.

5. Simplifying this, we get 3d = 240, so d = 240/3 = 80 km.

6. So, the original distance he was supposed to cover was 80 km. But since he walked 20 km more at a speed of 15 km/hr, the total distance covered by him would be 80 km + 20 km = 100 km.