word problem has me stumped.

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mlov83
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word problem has me stumped.

Postby mlov83 » Sun Aug 12, 2012 1:11 pm

I have a word problem that i cant seem to figuered out. Can someone point me in the right direction.

A boat cruises 36mi against a 3mph current and 36 mi back in the direction of the same current. The round trip takes 5 hours what is the speed of the boat in still water?

I have drawns pictures look at other google examples and im afraid to say that im just stumped can someone help me figuered out this answer and explain how you got it?
Thanks

FWT
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Re: word problem has me stumped.

Postby FWT » Sun Aug 12, 2012 1:14 pm

mlov83 wrote:A boat cruises 36mi against a 3mph current and 36 mi back in the direction of the same current. The round trip takes 5 hours what is the speed of the boat in still water?

The 2nd example on this page shows exactly how to set this up.

mlov83
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Re: word problem has me stumped.

Postby mlov83 » Sun Aug 12, 2012 1:33 pm

fwt i have looked at these examples and i just cant see the relevance? I try setting up different ways but its just not making sense?.
Thanks for the response.

mlov83
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Re: word problem has me stumped.

Postby mlov83 » Sun Aug 12, 2012 2:13 pm

Here is what i have so far I'm i on the rigth track?
speed of boat against stream x-3
speed of boat with stream x+3
however i think my equation is wrong.
I end up with something like this?
36/x-3 = 5 but im not sure what i should be doing about the other side of the equation

mlov83
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Re: word problem has me stumped.

Postby mlov83 » Sun Aug 12, 2012 6:50 pm

ok the equation is this.

Code: Select all

36/x-3  +  36/x+3 = 5(x+3)(x-3)

hope this is helpful for someone else someday. thanks for the 1 response.

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stapel_eliz
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Postby stapel_eliz » Sun Aug 12, 2012 7:54 pm

mlov83 wrote:ok the equation is this.

Code: Select all

36/x-3  +  36/x+3 = 5(x+3)(x-3)

hope this is helpful for someone else someday. thanks for the 1 response.

The "distance" equation is "d = rt". The expression "36/(x - 3)" is "d/t" and stands for "(the distance going upstream)/(the rate going upstream)", which results in "d/r = t", or "the time going upstream". The second expression can be interpreted similarly.

What does "5(x + 3)(x - 3)" stand for? :wink:

mlov83
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Re: word problem has me stumped.

Postby mlov83 » Sun Aug 12, 2012 11:35 pm

(x+3)(x-3) is your lcd. Sorry i should have mentioned that in my 4 or 5th post.
when you multiply throught with the lcd
you end up with

Code: Select all

36+36 =  5(x+3)(x-3)

hope that makes sense

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stapel_eliz
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Postby stapel_eliz » Mon Aug 13, 2012 12:56 pm

mlov83 wrote:(x+3)(x-3) is your lcd. Sorry i should have mentioned that in my 4 or 5th post.

Yes. But what does the right-hand side of your equation stand for?

mlov83 wrote:when you multiply throught with the lcd
you end up with

Code: Select all

36+36 =  5(x+3)(x-3)

hope that makes sense

If your equation is as you had posted:

. . . . .

...then your equation stands for "(time for the first part) plus (time for the second part) equals (time for the total) multiplied by (the LCD of ??)". What sense does that make?

Instead, try using the set-up method and logic outlined in the lesson at the link provided earlier. This will let you set up a logical equation, being "(part of the time) plus (the rest of the time) equals (the total time)".

Solve that equation, and you'll get an answer that works in the original exercise! :wink:


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