SOLUTION: A Johnson motorboat goes 5 miles upstream in the same time it requires to go 7 miles downstream. If the river flows at 2mph, find the speed of the boat in still water.

Question 987007: A Johnson motorboat goes 5 miles upstream in the same time it requires to go 7 miles downstream. If the river flows at 2mph, find the speed of the boat in still water.

Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39617) (Show Source): You can put this solution on YOUR website!
More general:
A Johnson motorboat goes miles upstream in the same time it requires to go miles downstream. If the river flows at s mph, find the speed r of the boat in still water.

Direction rate time distance upstream r-c t downstream r+c t Direction rate time distance upstream r-c downstream r+c

The time quantities were described as equal.

Their reciprocals are also equal (not the only strategy)...

Evaluate the boat speed r according to
.
Answer by MathTherapy(10552) (Show Source): You can put this solution on YOUR website!

A Johnson motorboat goes 5 miles upstream in the same time it requires to go 7 miles downstream. If the river flows at 2mph, find the speed of the boat in still water.

Let speed of boat in still water be S
Then total speed upstream (boat in still water, less speed of river current) = S - 2
Total speed downstream (boat in still water, plus speed of river current) = S + 2
We then get:
7(S - 2) = 5(S + 2) -------- Cross-multiplying
7S - 14 = 5S + 10
7S - 5S = 10 + 14
2S = 24
S, or speed of boat in still water = , or mph
RELATED QUESTIONS
A motorboat goes 5 miles upstream in the same time it requires to go 7 miles downstream. (answered by longjonsilver)
A motorboat goes 5 miles upstream in the same time it requires to go 7 miles downstream.... (answered by atif.muhammad)
A motorboat goes 5 miles upstream in the same time it requires to 7 miles downstream. If... (answered by mananth)
a motor boat goes 5 miles upstream in the same time it requires to go 7 miles downstream. (answered by mananth)
A motorboat goes 5 miles upstream in the same time it requires to go 7 miles downsteam.... (answered by lwsshak3)
A kayaker can travel 1.2 miles downstream in the same time it takes him to go 0.4 miles... (answered by ankor@dixie-net.com)
The river is moving at 5 miles per hour. A boat can travel 5 miles upstream in the same... (answered by robertb)
A motorboat goes 8 miles downstream, on a river, in 20 minutes. It takes 30 minutes for... (answered by mananth)
A motorboat can go 48 miles downstream on a river in 1 hour. It takes 1.5 hours for this... (answered by ewatrrr)