The speed of sailing against the current is slower than before because it is pulled down by the speed of the current (which can be understood as "power"). When the speed of the water flow is high, how much does it decrease? When the current speed = the ship speed, the ship will not run! If the current is faster than the boat, the boat will run backwards. Similarly, when driving downstream, the speed of water is "helpful". How fast the water is, the speed of the ship will increase.

Therefore, when the countercurrent speed is 28, the original speed of the ship (the speed in still water) is 28+2 = 30 km/h.

The downstream speed is the original speed (that is, the speed in still water)+water speed = 30+2 = 32km/h.

Some mathematical problems can be solved by formulas or described by language.

The topic of changing water is described in language: 16 empty bottles can be changed for 4 bottles of water, 1 bottles can be changed after drinking. * * * Change 5 bottles of water.