# Thread: Boat in Still Water

1. ## Boat in Still Water

Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water?

2. Originally Posted by magentarita
Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water?
Let the speed in still water be $\displaystyle x$ mph
When it travels upstream its speed= $\displaystyle x-4$ mph
Time taken to go upstream= $\displaystyle \frac{5}{x-4}$ h
Speed in downstream = $\displaystyle x+4$ mph
Time taken to go downstream or time taken to return back= $\displaystyle \frac{5}{x+4}$ h
And 20 min $\displaystyle = \frac{20}{60}=\frac{1}{3}$ hrs
But according to question...

$\displaystyle \frac{5}{x-4} -\frac{5}{x+4}=\frac{1}{3}$

Solve it and you will get the answer

3. ## wow.....

Originally Posted by great_math
Let the speed in still water be $\displaystyle x$ mph
When it travels upstream its speed= $\displaystyle x-4$ mph
Time taken to go upstream= $\displaystyle \frac{5}{x-4}$ h
Speed in downstream = $\displaystyle x+4$ mph
Time taken to go downstream or time taken to return back= $\displaystyle \frac{5}{x+4}$ h
And 20 min $\displaystyle = \frac{20}{60}=\frac{1}{3}$ hrs
But according to question...

$\displaystyle \frac{5}{x-4} -\frac{5}{x+4}=\frac{1}{3}$

Solve it and you will get the answer
You were able to come up with the right equation without creating a chart. Interesting.

4. Originally Posted by magentarita
You were able to come up with the right equation without creating a chart. Interesting.
The only thing that is to be kept in mind while doing this question is that:

when upstream subtract the speed of flow of water from the speed in still water and add when downstream

5. ## ok..........

Originally Posted by great_math
The only thing that is to be kept in mind while doing this question is that:

when upstream subtract the speed of flow of water from the speed in still water and add when downstream
Thank you for the input.