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Help with algebra problem

hellomynameisbob
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9/19/2012 2:37:04 PM
Posted: 4 years ago
There is a boat going from point A to B. It is 180 km from A to B. From point A to B is going downstream, so it only takes 10 hours. To get from point B to A, is upstream so it takes 15 hours. It rains so the river moves faster, and point A to B only takes 9 hours now. Now, how long will it take to get from point B to point A? Can you please help me with this? Explain how to do this problem.
bossyburrito
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9/19/2012 3:04:39 PM
Posted: 4 years ago
16 hours I guess. The rain makes downstream stronger, so upstream would take longer.
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bossyburrito
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9/19/2012 3:15:54 PM
Posted: 4 years ago
At 9/19/2012 3:04:39 PM, bossyburrito wrote:
16 hours I guess. The rain makes downstream stronger, so upstream would take longer.

I just realised how stupid my answer was...
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bossyburrito
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9/19/2012 3:19:03 PM
Posted: 4 years ago
A to b = 18 kph
B to a = 12 kph

A to b with rain = 20 kph
B to a with rain = 10 kph

180/10 = 18 hours
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"Some will sell their dreams for small desires
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Get caught in ticking traps
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AlwaysMoreThanYou
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9/19/2012 3:23:45 PM
Posted: 4 years ago
At 9/19/2012 2:37:04 PM, hellomynameisbob wrote:
There is a boat going from point A to B. It is 180 km from A to B. From point A to B is going downstream, so it only takes 10 hours. To get from point B to A, is upstream so it takes 15 hours. It rains so the river moves faster, and point A to B only takes 9 hours now. Now, how long will it take to get from point B to point A? Can you please help me with this? Explain how to do this problem.

By the time I'm done, someone else will probably have done it too, and much better.

The boat moves at rate x, and the river moves at rate y. When going downstream, the boat moves at rate x + y for 10 hours. The equation is:

10(x + y) = 180
x = 18 - y

Going upstream, the rate is x - y, and it takes 15 hours. The equation is:

15(x - y) = 180
x - y = 12
x = y + 12

Substitute:

18 - y = 12 + y
18 - 12 = 2y
6 = 2y
3 = y

x = 3 + 12
x = 15

In the next part, the current of the river (y) increases. To travel the same 180km, it now takes only 9 hours (downstream). We can preserve the x value, because the boat's speed does not change.

9(x + y) = 180
x + y = 20
15 + y = 20
y = 5

Now that we know the new rate of the current, we can solve for the time it takes to travel upstream against the current. The time it takes is a new variable, z.

z(15 - 5) = 180
10z = 180
z = 18

Therefore, it takes 18 hours to travel upstream against the new current.
'When the Spirit of truth comes, he will guide you into all the truth; for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come.' - John 16:13
AlwaysMoreThanYou
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9/19/2012 3:24:08 PM
Posted: 4 years ago
And I was right. Bossy beat me.
'When the Spirit of truth comes, he will guide you into all the truth; for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come.' - John 16:13
OberHerr
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9/19/2012 5:15:29 PM
Posted: 4 years ago
At 9/19/2012 5:13:55 PM, MilitaryAtheist wrote:
Who's the Fvcking douche who invented algebra?

http://en.wikipedia.org...
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bossyburrito
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9/19/2012 6:10:40 PM
Posted: 4 years ago
At 9/19/2012 3:24:08 PM, AlwaysMoreThanYou wrote:
And I was right. Bossy beat me.

I couldn't understand a thing you said.
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"Some will sell their dreams for small desires
Or lose the race to rats
Get caught in ticking traps
And start to dream of somewhere
To relax their restless flight
Somewhere out of a memory of lighted streets on quiet nights..."

~ Rush
lewis20
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9/19/2012 6:19:14 PM
Posted: 4 years ago
At 9/19/2012 5:16:47 PM, MilitaryAtheist wrote:
At 9/19/2012 5:15:29 PM, OberHerr wrote:
At 9/19/2012 5:13:55 PM, MilitaryAtheist wrote:
Who's the Fvcking douche who invented algebra?

http://en.wikipedia.org...

Had to be Arabic.

Aren't numbers? hah
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