From point A to point B, the distance between which is 20.5 km, a pedestrian left at a speed

From point A to point B, the distance between which is 20.5 km, a pedestrian left at a speed of 3 km / h. After 1 hour, the second pedestrian left point B to A at a speed of 4 km / h. How many hours after the exit of the second pedestrian they will meet.

1. We take as x the time of movement of the first pedestrian from point A to the meeting point.

2. (x -1) – time of movement of the second pedestrian from point B to the meeting point.

3. We compose and solve the equation:

3x + 4 (x – 1) = 20.5;

3x + 4x – 4 = 20.5;

7x = 24.5;

x = 3.5 hours.

4. Pedestrians will meet in 3.5 – 1 = 2.5 hours after the second pedestrian leaves point B.

Answer: pedestrians will meet 2.5 hours after the exit of the second pedestrian from point B.