Solution: Let the current speed be V meters per minute, the ship speed in still water be V meters per minute, and the speed of people in still water be V meters per minute: because V''=V'-V, the downstream V people =V'-V+V=V', therefore:

[300+3(V '-V)]/V ' = 300/V & lt； 1 & gt；

{(V '-V)[300+3(V '-V)]}/V ' = 300+3(V '-V)& lt； 2 & gt

Simplify with < 2 >:

V '-V = 300 & lt； 3 & gt

Replace < 1 > formula: 1200/V'=300/V, that is, V'/V=4.

Replace < 3 > formula: v' =100m v = 25m/min.