Distance problem: that is, the problem of walking and driving is generally called the trip problem by calculating distance, time and speed. To solve these problems, we must first understand the concepts of speed, time, distance, direction, speed sum and speed difference, and understand the relationship between them, and then answer them according to the laws of these problems.

The key and law of solving problems;

Walk in the opposite direction at the same time: distance = speed × time.

Walk in the opposite direction at the same time: distance = speed x meeting time.

Walking in the same direction at the same time (slow in front and fast in the back): catching up time = distance ÷ speed difference.

Walk in the same direction at the same time (slow behind, fast in front): distance = speed difference × time.

Example 1: A ship sailed from place A to place B along the river at a speed of 28 kilometers per hour. After arriving at B, sail against the current and return to A. The current is 2 hours longer than the current, and the known water speed is 4 kilometers per hour. What is the distance between a and b?

Analysis: This question needs to know the speed and time needed to go with the water, or the speed and time needed to go against the water. The speed and speed of the current are known, so it is not difficult to calculate the speed of the current, but the time required for the current is unknown, only that it takes 2 hours less than that of the current. Grasping this point, we can calculate the time needed to get from A to B with water, so that A and B can be calculated.

28-4× 2 = 20km

20× 2 = 40km

40(4×2)= 5 (hours)

28×5= 140 (km).

Comprehensive formula: (28-4×2)×2÷(4×2)×28.