Question 419568
Merle took half an hour to row 3km with the current.
 When he returned, he took 90 minutes.
 Find his rowing rate and the speed of the current.
;
Since you probably want the speed in km/hr, change the times to hrs
.5 hrs and 1.5 hrs 
:
Let r = his rowing speed in still water
Let c = rate of the current
then
(r+c) = his effective speed with the current
and
(r-c) = his effective speed against the current
:
Write a distance equation for each trip: time * speed = dist
.5(r+c) = 3; (downstream)
1.5(r-c) = 3; (upstream)
You can simplify both these equations, divide the 1st by .5, the 2nd by 1.5, results:
r + c = 6
r - c = 2
-------------adding these equations eliminates c, find r
2r = 8
r = 8/2
r = 4 km/hr is his rowing speed
:
Find the current using r + c = 6
4 + c = 6
c = 6 - 4
c = 2 km/hr is the current
:
:
Check solution in the 1st original equation
.5(4 + 2) = 3