SOLUTION: A motorboat can go 8 miles downstream on a river in 20 minutes. It takes 30 minutes to go upstream the same 8 miles. Find the speed of the current.

Question 615108: A motorboat can go 8 miles downstream on a river in 20 minutes. It takes 30 minutes to go upstream the same 8 miles. Find the speed of the current.
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
A motorboat can go 8 miles downstream on a river in 20 minutes. It takes 30 minutes to go upstream the same 8 miles. Find the speed of the current.
:
Let s = speed of the boat in still water
Let c = speed of the current
then
(s-c) = effective speed upstream
and
(s+c) = effective speed downstream
:
since we will wanting mph, change 20 min to 1/3 hr, and 30 min to 1/2 hr
:
Write a distance equation for each way; (dist = time * speed)
(s + c) = 8
(s - c) = 8
multiply the 1st equation by 3, the 2nd equation by 2:
s + c = 24
s - c = 16
---------- adding eliminates c, find s
2s = 40
s = 20 mph boat speed in still water
then
20 + c = 24
c = 24 - 20
c = 4 mph is the speed of the current
:
:
You can confirm this with the distance equation each way

RELATED QUESTIONS
A motorboat can go 8 miles downstream on a river in 20 minutes. It takes 30 minutes for... (answered by checkley77)

A motorboat can go 8 miles downstream on a river in 10 minutes. It takes 30 minutes for... (answered by scott8148)

a motorboat can go 8 miles downstream in 20 minutes. It takes the same motorboat 30... (answered by nerdybill,checkley77)

A motorboat can go 16 miles downstream on a river in 20 minutes. It takes 30 minutes for... (answered by josmiceli)

A motorboat can go 14 miles downstream on a river in 20 minutes. It takes 30 minutes for... (answered by checkley77)

Please help me solve this problem: A motorboat can go 14 miles downstream on a river... (answered by mananth)

A motorboat can go 12 miles downstream on a river in 20 minutes. It takes 30 minutes for... (answered by stanbon)

A motorboat goes 8 miles downstream, on a river, in 20 minutes. It takes 30 minutes for... (answered by mananth)