<PRE><B>Question 601587</B>
If a boat goes downstream 72 miles in 3 hours and upstream 60 miles in 6 hours, the rate of the river and the rate of the boat in still water respectively are:
**
let x=rate of speed of boat in still water
let c=rate of speed of current
net speed of boat downstream=x+c
net speed of boat upstream=x-c
distance = travel time*speed
..
3(x+c)=72
6(x-c)=72
..
3x+3c=72
6x-6c=72
..
6x+6c=144 (mult.by 2)
6x-6c=72
add
12x=216
x=18
6c=144-6x=36
c=6
ans:
rate of speed of boat in still water=18 mph
rate of speed of current=6 mph</PRE>