# Boat in Still Water

• Nov 25th 2008, 10:18 PM
magentarita
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?
• Nov 26th 2008, 08:13 AM
great_math
Quote:

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
• Nov 28th 2008, 05:00 AM
magentarita
wow.....
Quote:

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.
• Nov 28th 2008, 05:06 AM
great_math
Quote:

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
• Nov 28th 2008, 09:08 AM
magentarita
ok..........
Quote:

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.