Rusty has a boat goes 12 mi. an hour. Find the current speed of the river if he can go 3 mi. upstream in the same time as he goes 5 mi. downstream.
Please show work

Question

Rusty has a boat goes 12 mi. an hour.  Find the current speed of the river if he can go 3 mi. upstream in the same time as he goes  5 mi. downstream. 
Please show work

anonymous · Answer

your speed*time=distance traveled so:

3=(12-x)t
and
5=(12+x)t
solve for t in both equations
3/(12-x)=t
5/(12+x)=t
substitute:
3/(12-x)=5/(12+x)
cross multiply
3(12+x)=5(12-x)
36+3x=60-5x
8x=24
x=3
so stream current is 3 miles/hr downstream

anonymous · Answer

thats what I got. I just wanted a second opinion!!! Thanks!!!

anonymous · Answer

no prob