From points A and B, the distance between which is 21 km, both a pedestrian from B and a cyclist from

From points A and B, the distance between which is 21 km, both a pedestrian from B and a cyclist from A follow him and move at a speed: pedestrian 5 km / h, cyclist 12 km / h. How many kilometers will the distance between them decrease in 3 hours?

The solution of the problem:

1. Find out the speed of convergence, when moving in one direction:

12 – 5 = 7 km / h.

2. Determine how many km the distance between them will decrease in 3 hours:

2) 7 * 3 = 21 km.

Answer: the distance between them will decrease in 3 hours by 21 km, i.e. the cyclist will catch up with the pedestrian.