Question 921393
A paddle boat can move at a speed of 20km/h in still water. The boat is paddled 18km downstream in a river in the same time it takes to go 9km upstream. What is the speed of the river? 
***
let c=speed of the river current
20+c=speed of paddle boat downstream
20-c=speed of paddle boat upstream
travel time=distance/speed
..
{{{18/(20+c)=9/(20-c)}}}
18(20-c)=9(20+c)
360-18c=180+9c
27c=180
c=6 2/3=20/3
speed of the river current=20/3 km/hr